Are all final variables captured by anonymous classes?

up vote
6
down vote

favorite

I thought I knew the answer to this, but I can't find any confirmation after an hour or so of searching.

In this code:

public class Outer 

 // other code

 private void method1() 
 final SomeObject obj1 = new SomeObject(...);
 final SomeObject obj2 = new SomeObject(...);
 someManager.registerCallback(new SomeCallbackClass() 
 @Override
 public void onEvent() 
 System.out.println(obj1.getName());
 
 );

Assume that registerCallback saves its parameter somewhere, so that the object of the anonymous subclass will live for a while. Obviously this object has to maintain a reference to obj1 so that onEvent will work if it is called.

But given that the object doesn't use obj2, does it still maintain a reference to obj2, so that obj2 can't be garbage-collected while the object lives? I was under the impression that all visible final (or effectively final) local variables and parameters were captured and thus couldn't be GC'ed as long as the object was alive, but I can't find anything that says one way or the other.

Is it implementation-dependent?

Is there a section in the JLS that answers this? I wasn't able to find the answer there.

asked 41 mins ago

ajb

26.5k33257

How do you know that obj2 is bound to callback$x? You have seen it in bytecode?
â€“Â Antoniossss
32 mins ago

1

"Is it implementation-dependent?" Technically, yes. There is no reason for the anonymous class to capture obj2, but there is no reason it can't.
â€“Â Andy Turner
26 mins ago

I think a good reason it would not capture obj2 as a matter of course is that you can have multiple anonymous classes declared in a method: one of those classes might refer to obj1 only, whilst another might refer to obj2 only. It wouldn't be sensible for both classes to capture both variables.
â€“Â Andy Turner
8 mins ago

add a commentÂ |Â

up vote
6
down vote

favorite

I thought I knew the answer to this, but I can't find any confirmation after an hour or so of searching.

In this code:

public class Outer 

 // other code

 private void method1() 
 final SomeObject obj1 = new SomeObject(...);
 final SomeObject obj2 = new SomeObject(...);
 someManager.registerCallback(new SomeCallbackClass() 
 @Override
 public void onEvent() 
 System.out.println(obj1.getName());
 
 );

Is it implementation-dependent?

Is there a section in the JLS that answers this? I wasn't able to find the answer there.

asked 41 mins ago

ajb

26.5k33257

How do you know that obj2 is bound to callback$x? You have seen it in bytecode?
â€“Â Antoniossss
32 mins ago

1

"Is it implementation-dependent?" Technically, yes. There is no reason for the anonymous class to capture obj2, but there is no reason it can't.
â€“Â Andy Turner
26 mins ago

I think a good reason it would not capture obj2 as a matter of course is that you can have multiple anonymous classes declared in a method: one of those classes might refer to obj1 only, whilst another might refer to obj2 only. It wouldn't be sensible for both classes to capture both variables.
â€“Â Andy Turner
8 mins ago

add a commentÂ |Â

up vote
6
down vote

favorite

I thought I knew the answer to this, but I can't find any confirmation after an hour or so of searching.

In this code:

public class Outer 

 // other code

 private void method1() 
 final SomeObject obj1 = new SomeObject(...);
 final SomeObject obj2 = new SomeObject(...);
 someManager.registerCallback(new SomeCallbackClass() 
 @Override
 public void onEvent() 
 System.out.println(obj1.getName());
 
 );

Is it implementation-dependent?

Is there a section in the JLS that answers this? I wasn't able to find the answer there.

asked 41 mins ago

ajb

26.5k33257

I thought I knew the answer to this, but I can't find any confirmation after an hour or so of searching.

In this code:

public class Outer 

 // other code

 private void method1() 
 final SomeObject obj1 = new SomeObject(...);
 final SomeObject obj2 = new SomeObject(...);
 someManager.registerCallback(new SomeCallbackClass() 
 @Override
 public void onEvent() 
 System.out.println(obj1.getName());
 
 );

Is it implementation-dependent?

Is there a section in the JLS that answers this? I wasn't able to find the answer there.

java anonymous-class

asked 41 mins ago

ajb

26.5k33257

asked 41 mins ago

ajb

26.5k33257

asked 41 mins ago

ajb

26.5k33257

asked 41 mins ago

ajb

26.5k33257

asked 41 mins ago

ajb

26.5k33257

How do you know that obj2 is bound to callback$x? You have seen it in bytecode?
â€“Â Antoniossss
32 mins ago

1

"Is it implementation-dependent?" Technically, yes. There is no reason for the anonymous class to capture obj2, but there is no reason it can't.
â€“Â Andy Turner
26 mins ago

I think a good reason it would not capture obj2 as a matter of course is that you can have multiple anonymous classes declared in a method: one of those classes might refer to obj1 only, whilst another might refer to obj2 only. It wouldn't be sensible for both classes to capture both variables.
â€“Â Andy Turner
8 mins ago

add a commentÂ |Â

How do you know that obj2 is bound to callback$x? You have seen it in bytecode?
â€“Â Antoniossss
32 mins ago

1

"Is it implementation-dependent?" Technically, yes. There is no reason for the anonymous class to capture obj2, but there is no reason it can't.
â€“Â Andy Turner
26 mins ago

I think a good reason it would not capture obj2 as a matter of course is that you can have multiple anonymous classes declared in a method: one of those classes might refer to obj1 only, whilst another might refer to obj2 only. It wouldn't be sensible for both classes to capture both variables.
â€“Â Andy Turner
8 mins ago

How do you know that obj2 is bound to callback$x? You have seen it in bytecode?
â€“Â Antoniossss
32 mins ago

"Is it implementation-dependent?" Technically, yes. There is no reason for the anonymous class to capture obj2, but there is no reason it can't.
â€“Â Andy Turner
26 mins ago

I think a good reason it would not capture obj2 as a matter of course is that you can have multiple anonymous classes declared in a method: one of those classes might refer to obj1 only, whilst another might refer to obj2 only. It wouldn't be sensible for both classes to capture both variables.
â€“Â Andy Turner
8 mins ago

add a commentÂ |Â

5 Answers
5

active

oldest

votes

up vote
4
down vote

Only obj1 is captured.

Logically, the anonymous class is implemented as a normal class something like this:

class Anonymous1 extends SomeCallbackClass 
 private final Outer _outer;
 private final SomeObject obj1;
 Anonymous1(Outer _outer, SomeObject obj1) 
 this._outer = _outer;
 this.obj1 = obj1;
 
 @Override
 public void onEvent() 
 System.out.println(this.obj1.getName());
 
);

^{Note that an anonymous class is always an inner class, so it will always maintain a reference to the outer class, even if it doesn't need it. I don't know if later versions of the compiler have optimized that away, but I don't think so. It is a potential cause of memory leaks.}

The use of it becomes:

someManager.registerCallback(new Anonymous1(this, obj1));

As you can see, the reference value of obj1 is copied (pass-by-value).

There is technically no reason for obj1 to be final, whether declared final or effectively final (Java 8+), except that if it wasn't and you change the value, the copy wouldn't change, causing bugs because you expected the value to change, given that the copying is a hidden action. To prevent programmer confusion, they decided that obj1 must be final, so you can never become confused about that behavior.

edited 25 mins ago

answered 32 mins ago

Andreas

72.3k454115

2

Worth mentioning that since Java 8 the restriction on having to explicitly declare final has been lifted. The JLS now talks about "effectively final" variables.
â€“Â Boris the Spider
28 mins ago

it is not only logically, it is almost exactly that what the compiler does (Java 8 and 11), just the fields are named differently [:-)
â€“Â Carlos Heuberger
2 mins ago

add a commentÂ |Â

up vote
2
down vote

The only especially relevant section of the language spec that I can find is JLS Sec 8.1.3:

Any local variable, formal parameter, or exception parameter used but not declared in an inner class must either be declared final or be effectively final (Ã‚Â§4.12.4), or a compile-time error occurs where the use is attempted.)

(Anonymous classes are inner classes)

It does not specify anything about which variables the anonymous class should capture, or how that capturing should be implemented.

I think it is reasonable to infer from this that implementations need not capture variables that aren't referenced in the inner class; but it doesn't say they can't.

answered 13 mins ago

Andy Turner

77.3k876124

add a commentÂ |Â

up vote
1
down vote

I was curious and surprised by your statement that much (why would compiler do such thing???), that I had to check it myself. So I made simple example like this

public class test 
 private static Object holder;

 private void method1() 
 final Object obj1 = new Object();
 final Object obj2 = new Object();
 holder = new ActionListener() 
 @Override
 public void actionPerformed(ActionEvent e) 
 System.out.println(obj1);
 
 ;

And resulted with following bytecode for of method1

 private method1()V
 L0
 LINENUMBER 8 L0
 NEW java/lang/Object
 DUP
 INVOKESPECIAL java/lang/Object.<init> ()V
 ASTORE 1
 L1
 LINENUMBER 9 L1
 NEW java/lang/Object
 DUP
 INVOKESPECIAL java/lang/Object.<init> ()V
 ASTORE 2
 L2
 LINENUMBER 10 L2
 NEW test$1
 DUP
 ALOAD 0
 ALOAD 1
 INVOKESPECIAL test$1.<init> (Ltest;Ljava/lang/Object;)V
 PUTSTATIC test.holder : Ljava/lang/Object;

Which means:

L0 - store first final with idx 1 (ASTORE 1)

L1 - store second final with idx 2(that one is not used in anon class) (ASTORE 2)

L2 - create new test$1 with argumets (ALOAD 0) this and obj1 (ALOAD 1)

So I have no idea, how did you get to the conclusion that obj2 is passed to anonymous class instance, but it was simply wrong. IDK if it is compiler dependent, but as for what other has stated, it is not impossible.

answered 14 mins ago

Antoniossss

14.5k12149

add a commentÂ |Â

up vote
-1
down vote

Even though GC is not deterministic, I think this is testable using java.lang.ref.WeakReference:

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;

public class Outer 

 // other code

 private Reference<Object> obj1Ref;
 private Reference<Object> obj2Ref;

 private void method1() 
 final Object obj1 = new Object();
 final Object obj2 = new Object();

 obj1Ref = new WeakReference<Object>(obj1);
 obj2Ref = new WeakReference<Object>(obj2);

 Manager someManager = new Manager();
 someManager.registerCallback(new SomeCallbackClass() 
 @Override
 public void onEvent() 
 System.out.println(obj1.hashCode());
 
 );
 

 // To be called after method1() finishes but before onEvent() get's called.
 public void checkReferences () 

 Object object1 = obj1Ref.get();
 System.out.println("obj1 is still alive: " + object1 != null);

 Object object2 = obj1Ref.get();
 System.out.println("obj2 is still alive: " + object2 != null);

answered 13 mins ago

aka-one

1,05118

add a commentÂ |Â

up vote
-2
down vote

This code displays 10, it's unaffected by garbage collector:

public class HelloWorld

 public static void main(String args)
 Outer q = new Outer();

 System.gc();
 System.runFinalization();

 q.method1().ok(4,1);



 

 interface Ok
 
 public void ok(int a, int b);
 


class Outer 
 private final int obj1 = 5;
 public Ok method1() 

 Ok justDoIt = new Ok()
 public void ok(int a, int b)
 
 System.out.println(obj1+a+b);
 


 ;

 return justDoIt;

To be honest I don't exactly understand your question.

But, a final variable or a "non-final" variable for GC are the same things. The only restriction is that when you try to set it again you are blocked.

Think of a final variable this way:

public class HelloWorld

 public static void main(String args)
 Final<Integer> q = new Final();
 q.set(5);
 System.out.println(q.get());

 q.set(10); // ERROR

 




class Final <T>

 private T variable;
 private Boolean setted=false;

 public void set(T value) throws Error
 if(setted) 
 throw new Error();
 

 variable=value;
 setted = true;
 

 public T get()return variable;

And since you are creating a reference of the variable in the anonymous class, as long as you have the parent class referenced somewhere, it will linger and not be touched by gc. Even if the method is anonymous (or not), you still created a reference (pointer) to it

answered 10 mins ago

Nertan Lucian

9219

If you don't understand the OP why would you post an answer to this question when it is already answered by 4 different people.
â€“Â Rab
9 mins ago

OP meant that he thought that even obj2 is not used in anon class it still holds reference to it (which is false btw). Its not about final or not declarations.
â€“Â Antoniossss
9 mins ago

I answered base on title, obj2 in op post has no outside reference as long as Outer class is not instantiated
â€“Â Nertan Lucian
6 mins ago

You are missing the point and if you answered base on title, it is still off topic IMHO.
â€“Â Antoniossss
5 mins ago

add a commentÂ |Â

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5 Answers
5

active

oldest

votes

5 Answers
5

active

oldest

votes

up vote
4
down vote

Only obj1 is captured.

Logically, the anonymous class is implemented as a normal class something like this:

class Anonymous1 extends SomeCallbackClass 
 private final Outer _outer;
 private final SomeObject obj1;
 Anonymous1(Outer _outer, SomeObject obj1) 
 this._outer = _outer;
 this.obj1 = obj1;
 
 @Override
 public void onEvent() 
 System.out.println(this.obj1.getName());
 
);

The use of it becomes:

someManager.registerCallback(new Anonymous1(this, obj1));

As you can see, the reference value of obj1 is copied (pass-by-value).

edited 25 mins ago

answered 32 mins ago

Andreas

72.3k454115

2

Worth mentioning that since Java 8 the restriction on having to explicitly declare final has been lifted. The JLS now talks about "effectively final" variables.
â€“Â Boris the Spider
28 mins ago

it is not only logically, it is almost exactly that what the compiler does (Java 8 and 11), just the fields are named differently [:-)
â€“Â Carlos Heuberger
2 mins ago

add a commentÂ |Â

up vote
4
down vote

Only obj1 is captured.

Logically, the anonymous class is implemented as a normal class something like this:

class Anonymous1 extends SomeCallbackClass 
 private final Outer _outer;
 private final SomeObject obj1;
 Anonymous1(Outer _outer, SomeObject obj1) 
 this._outer = _outer;
 this.obj1 = obj1;
 
 @Override
 public void onEvent() 
 System.out.println(this.obj1.getName());
 
);

The use of it becomes:

someManager.registerCallback(new Anonymous1(this, obj1));

As you can see, the reference value of obj1 is copied (pass-by-value).

edited 25 mins ago

answered 32 mins ago

Andreas

72.3k454115

2

Worth mentioning that since Java 8 the restriction on having to explicitly declare final has been lifted. The JLS now talks about "effectively final" variables.
â€“Â Boris the Spider
28 mins ago

it is not only logically, it is almost exactly that what the compiler does (Java 8 and 11), just the fields are named differently [:-)
â€“Â Carlos Heuberger
2 mins ago

add a commentÂ |Â

up vote
4
down vote

Only obj1 is captured.

Logically, the anonymous class is implemented as a normal class something like this:

class Anonymous1 extends SomeCallbackClass 
 private final Outer _outer;
 private final SomeObject obj1;
 Anonymous1(Outer _outer, SomeObject obj1) 
 this._outer = _outer;
 this.obj1 = obj1;
 
 @Override
 public void onEvent() 
 System.out.println(this.obj1.getName());
 
);

The use of it becomes:

someManager.registerCallback(new Anonymous1(this, obj1));

As you can see, the reference value of obj1 is copied (pass-by-value).

edited 25 mins ago

answered 32 mins ago

Andreas

72.3k454115

Only obj1 is captured.

Logically, the anonymous class is implemented as a normal class something like this:

class Anonymous1 extends SomeCallbackClass 
 private final Outer _outer;
 private final SomeObject obj1;
 Anonymous1(Outer _outer, SomeObject obj1) 
 this._outer = _outer;
 this.obj1 = obj1;
 
 @Override
 public void onEvent() 
 System.out.println(this.obj1.getName());
 
);

The use of it becomes:

someManager.registerCallback(new Anonymous1(this, obj1));

As you can see, the reference value of obj1 is copied (pass-by-value).

edited 25 mins ago

answered 32 mins ago

Andreas

72.3k454115

edited 25 mins ago

answered 32 mins ago

Andreas

72.3k454115

answered 32 mins ago

Andreas

72.3k454115

answered 32 mins ago

Andreas

72.3k454115

2

Worth mentioning that since Java 8 the restriction on having to explicitly declare final has been lifted. The JLS now talks about "effectively final" variables.
â€“Â Boris the Spider
28 mins ago

it is not only logically, it is almost exactly that what the compiler does (Java 8 and 11), just the fields are named differently [:-)
â€“Â Carlos Heuberger
2 mins ago

add a commentÂ |Â

2

Worth mentioning that since Java 8 the restriction on having to explicitly declare final has been lifted. The JLS now talks about "effectively final" variables.
â€“Â Boris the Spider
28 mins ago

it is not only logically, it is almost exactly that what the compiler does (Java 8 and 11), just the fields are named differently [:-)
â€“Â Carlos Heuberger
2 mins ago

Worth mentioning that since Java 8 the restriction on having to explicitly declare final has been lifted. The JLS now talks about "effectively final" variables.
â€“Â Boris the Spider
28 mins ago

it is not only logically, it is almost exactly that what the compiler does (Java 8 and 11), just the fields are named differently [:-)
â€“Â Carlos Heuberger
2 mins ago

add a commentÂ |Â

up vote
2
down vote

The only especially relevant section of the language spec that I can find is JLS Sec 8.1.3:

Any local variable, formal parameter, or exception parameter used but not declared in an inner class must either be declared final or be effectively final (Ã‚Â§4.12.4), or a compile-time error occurs where the use is attempted.)

(Anonymous classes are inner classes)

It does not specify anything about which variables the anonymous class should capture, or how that capturing should be implemented.

I think it is reasonable to infer from this that implementations need not capture variables that aren't referenced in the inner class; but it doesn't say they can't.

answered 13 mins ago

Andy Turner

77.3k876124

add a commentÂ |Â

up vote
2
down vote

The only especially relevant section of the language spec that I can find is JLS Sec 8.1.3:

Any local variable, formal parameter, or exception parameter used but not declared in an inner class must either be declared final or be effectively final (Ã‚Â§4.12.4), or a compile-time error occurs where the use is attempted.)

(Anonymous classes are inner classes)

It does not specify anything about which variables the anonymous class should capture, or how that capturing should be implemented.

I think it is reasonable to infer from this that implementations need not capture variables that aren't referenced in the inner class; but it doesn't say they can't.

answered 13 mins ago

Andy Turner

77.3k876124

add a commentÂ |Â

up vote
2
down vote

The only especially relevant section of the language spec that I can find is JLS Sec 8.1.3:

Any local variable, formal parameter, or exception parameter used but not declared in an inner class must either be declared final or be effectively final (Ã‚Â§4.12.4), or a compile-time error occurs where the use is attempted.)

(Anonymous classes are inner classes)

It does not specify anything about which variables the anonymous class should capture, or how that capturing should be implemented.

I think it is reasonable to infer from this that implementations need not capture variables that aren't referenced in the inner class; but it doesn't say they can't.

answered 13 mins ago

Andy Turner

77.3k876124

The only especially relevant section of the language spec that I can find is JLS Sec 8.1.3:

Any local variable, formal parameter, or exception parameter used but not declared in an inner class must either be declared final or be effectively final (Ã‚Â§4.12.4), or a compile-time error occurs where the use is attempted.)

(Anonymous classes are inner classes)

It does not specify anything about which variables the anonymous class should capture, or how that capturing should be implemented.

I think it is reasonable to infer from this that implementations need not capture variables that aren't referenced in the inner class; but it doesn't say they can't.

answered 13 mins ago

Andy Turner

77.3k876124

answered 13 mins ago

Andy Turner

77.3k876124

answered 13 mins ago

Andy Turner

77.3k876124

answered 13 mins ago

Andy Turner

77.3k876124

add a commentÂ |Â

up vote
1
down vote

I was curious and surprised by your statement that much (why would compiler do such thing???), that I had to check it myself. So I made simple example like this

public class test 
 private static Object holder;

 private void method1() 
 final Object obj1 = new Object();
 final Object obj2 = new Object();
 holder = new ActionListener() 
 @Override
 public void actionPerformed(ActionEvent e) 
 System.out.println(obj1);
 
 ;

And resulted with following bytecode for of method1

 private method1()V
 L0
 LINENUMBER 8 L0
 NEW java/lang/Object
 DUP
 INVOKESPECIAL java/lang/Object.<init> ()V
 ASTORE 1
 L1
 LINENUMBER 9 L1
 NEW java/lang/Object
 DUP
 INVOKESPECIAL java/lang/Object.<init> ()V
 ASTORE 2
 L2
 LINENUMBER 10 L2
 NEW test$1
 DUP
 ALOAD 0
 ALOAD 1
 INVOKESPECIAL test$1.<init> (Ltest;Ljava/lang/Object;)V
 PUTSTATIC test.holder : Ljava/lang/Object;

Which means:

L0 - store first final with idx 1 (ASTORE 1)

L1 - store second final with idx 2(that one is not used in anon class) (ASTORE 2)

L2 - create new test$1 with argumets (ALOAD 0) this and obj1 (ALOAD 1)

answered 14 mins ago

Antoniossss

14.5k12149

add a commentÂ |Â

up vote
1
down vote

I was curious and surprised by your statement that much (why would compiler do such thing???), that I had to check it myself. So I made simple example like this

public class test 
 private static Object holder;

 private void method1() 
 final Object obj1 = new Object();
 final Object obj2 = new Object();
 holder = new ActionListener() 
 @Override
 public void actionPerformed(ActionEvent e) 
 System.out.println(obj1);
 
 ;

And resulted with following bytecode for of method1

 private method1()V
 L0
 LINENUMBER 8 L0
 NEW java/lang/Object
 DUP
 INVOKESPECIAL java/lang/Object.<init> ()V
 ASTORE 1
 L1
 LINENUMBER 9 L1
 NEW java/lang/Object
 DUP
 INVOKESPECIAL java/lang/Object.<init> ()V
 ASTORE 2
 L2
 LINENUMBER 10 L2
 NEW test$1
 DUP
 ALOAD 0
 ALOAD 1
 INVOKESPECIAL test$1.<init> (Ltest;Ljava/lang/Object;)V
 PUTSTATIC test.holder : Ljava/lang/Object;

Which means:

L0 - store first final with idx 1 (ASTORE 1)

L1 - store second final with idx 2(that one is not used in anon class) (ASTORE 2)

L2 - create new test$1 with argumets (ALOAD 0) this and obj1 (ALOAD 1)

answered 14 mins ago

Antoniossss

14.5k12149

add a commentÂ |Â

up vote
1
down vote

I was curious and surprised by your statement that much (why would compiler do such thing???), that I had to check it myself. So I made simple example like this

public class test 
 private static Object holder;

 private void method1() 
 final Object obj1 = new Object();
 final Object obj2 = new Object();
 holder = new ActionListener() 
 @Override
 public void actionPerformed(ActionEvent e) 
 System.out.println(obj1);
 
 ;

And resulted with following bytecode for of method1

 private method1()V
 L0
 LINENUMBER 8 L0
 NEW java/lang/Object
 DUP
 INVOKESPECIAL java/lang/Object.<init> ()V
 ASTORE 1
 L1
 LINENUMBER 9 L1
 NEW java/lang/Object
 DUP
 INVOKESPECIAL java/lang/Object.<init> ()V
 ASTORE 2
 L2
 LINENUMBER 10 L2
 NEW test$1
 DUP
 ALOAD 0
 ALOAD 1
 INVOKESPECIAL test$1.<init> (Ltest;Ljava/lang/Object;)V
 PUTSTATIC test.holder : Ljava/lang/Object;

Which means:

L0 - store first final with idx 1 (ASTORE 1)

L1 - store second final with idx 2(that one is not used in anon class) (ASTORE 2)

L2 - create new test$1 with argumets (ALOAD 0) this and obj1 (ALOAD 1)

answered 14 mins ago

Antoniossss

14.5k12149

I was curious and surprised by your statement that much (why would compiler do such thing???), that I had to check it myself. So I made simple example like this

public class test 
 private static Object holder;

 private void method1() 
 final Object obj1 = new Object();
 final Object obj2 = new Object();
 holder = new ActionListener() 
 @Override
 public void actionPerformed(ActionEvent e) 
 System.out.println(obj1);
 
 ;

And resulted with following bytecode for of method1

 private method1()V
 L0
 LINENUMBER 8 L0
 NEW java/lang/Object
 DUP
 INVOKESPECIAL java/lang/Object.<init> ()V
 ASTORE 1
 L1
 LINENUMBER 9 L1
 NEW java/lang/Object
 DUP
 INVOKESPECIAL java/lang/Object.<init> ()V
 ASTORE 2
 L2
 LINENUMBER 10 L2
 NEW test$1
 DUP
 ALOAD 0
 ALOAD 1
 INVOKESPECIAL test$1.<init> (Ltest;Ljava/lang/Object;)V
 PUTSTATIC test.holder : Ljava/lang/Object;

Which means:

L0 - store first final with idx 1 (ASTORE 1)

L1 - store second final with idx 2(that one is not used in anon class) (ASTORE 2)

L2 - create new test$1 with argumets (ALOAD 0) this and obj1 (ALOAD 1)

answered 14 mins ago

Antoniossss

14.5k12149

answered 14 mins ago

Antoniossss

14.5k12149

answered 14 mins ago

Antoniossss

14.5k12149

answered 14 mins ago

Antoniossss

14.5k12149

add a commentÂ |Â

up vote
-1
down vote

Even though GC is not deterministic, I think this is testable using java.lang.ref.WeakReference:

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;

public class Outer 

 // other code

 private Reference<Object> obj1Ref;
 private Reference<Object> obj2Ref;

 private void method1() 
 final Object obj1 = new Object();
 final Object obj2 = new Object();

 obj1Ref = new WeakReference<Object>(obj1);
 obj2Ref = new WeakReference<Object>(obj2);

 Manager someManager = new Manager();
 someManager.registerCallback(new SomeCallbackClass() 
 @Override
 public void onEvent() 
 System.out.println(obj1.hashCode());
 
 );
 

 // To be called after method1() finishes but before onEvent() get's called.
 public void checkReferences () 

 Object object1 = obj1Ref.get();
 System.out.println("obj1 is still alive: " + object1 != null);

 Object object2 = obj1Ref.get();
 System.out.println("obj2 is still alive: " + object2 != null);

answered 13 mins ago

aka-one

1,05118

add a commentÂ |Â

up vote
-1
down vote

Even though GC is not deterministic, I think this is testable using java.lang.ref.WeakReference:

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;

public class Outer 

 // other code

 private Reference<Object> obj1Ref;
 private Reference<Object> obj2Ref;

 private void method1() 
 final Object obj1 = new Object();
 final Object obj2 = new Object();

 obj1Ref = new WeakReference<Object>(obj1);
 obj2Ref = new WeakReference<Object>(obj2);

 Manager someManager = new Manager();
 someManager.registerCallback(new SomeCallbackClass() 
 @Override
 public void onEvent() 
 System.out.println(obj1.hashCode());
 
 );
 

 // To be called after method1() finishes but before onEvent() get's called.
 public void checkReferences () 

 Object object1 = obj1Ref.get();
 System.out.println("obj1 is still alive: " + object1 != null);

 Object object2 = obj1Ref.get();
 System.out.println("obj2 is still alive: " + object2 != null);

answered 13 mins ago

aka-one

1,05118

add a commentÂ |Â

up vote
-1
down vote

Even though GC is not deterministic, I think this is testable using java.lang.ref.WeakReference:

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;

public class Outer 

 // other code

 private Reference<Object> obj1Ref;
 private Reference<Object> obj2Ref;

 private void method1() 
 final Object obj1 = new Object();
 final Object obj2 = new Object();

 obj1Ref = new WeakReference<Object>(obj1);
 obj2Ref = new WeakReference<Object>(obj2);

 Manager someManager = new Manager();
 someManager.registerCallback(new SomeCallbackClass() 
 @Override
 public void onEvent() 
 System.out.println(obj1.hashCode());
 
 );
 

 // To be called after method1() finishes but before onEvent() get's called.
 public void checkReferences () 

 Object object1 = obj1Ref.get();
 System.out.println("obj1 is still alive: " + object1 != null);

 Object object2 = obj1Ref.get();
 System.out.println("obj2 is still alive: " + object2 != null);

answered 13 mins ago

aka-one

1,05118

Even though GC is not deterministic, I think this is testable using java.lang.ref.WeakReference:

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;

public class Outer 

 // other code

 private Reference<Object> obj1Ref;
 private Reference<Object> obj2Ref;

 private void method1() 
 final Object obj1 = new Object();
 final Object obj2 = new Object();

 obj1Ref = new WeakReference<Object>(obj1);
 obj2Ref = new WeakReference<Object>(obj2);

 Manager someManager = new Manager();
 someManager.registerCallback(new SomeCallbackClass() 
 @Override
 public void onEvent() 
 System.out.println(obj1.hashCode());
 
 );
 

 // To be called after method1() finishes but before onEvent() get's called.
 public void checkReferences () 

 Object object1 = obj1Ref.get();
 System.out.println("obj1 is still alive: " + object1 != null);

 Object object2 = obj1Ref.get();
 System.out.println("obj2 is still alive: " + object2 != null);

answered 13 mins ago

aka-one

1,05118

answered 13 mins ago

aka-one

1,05118

answered 13 mins ago

aka-one

1,05118

answered 13 mins ago

aka-one

1,05118

add a commentÂ |Â

up vote
-2
down vote

This code displays 10, it's unaffected by garbage collector:

public class HelloWorld

 public static void main(String args)
 Outer q = new Outer();

 System.gc();
 System.runFinalization();

 q.method1().ok(4,1);



 

 interface Ok
 
 public void ok(int a, int b);
 


class Outer 
 private final int obj1 = 5;
 public Ok method1() 

 Ok justDoIt = new Ok()
 public void ok(int a, int b)
 
 System.out.println(obj1+a+b);
 


 ;

 return justDoIt;

To be honest I don't exactly understand your question.

But, a final variable or a "non-final" variable for GC are the same things. The only restriction is that when you try to set it again you are blocked.

Think of a final variable this way:

public class HelloWorld

 public static void main(String args)
 Final<Integer> q = new Final();
 q.set(5);
 System.out.println(q.get());

 q.set(10); // ERROR

 




class Final <T>

 private T variable;
 private Boolean setted=false;

 public void set(T value) throws Error
 if(setted) 
 throw new Error();
 

 variable=value;
 setted = true;
 

 public T get()return variable;

answered 10 mins ago

Nertan Lucian

9219

If you don't understand the OP why would you post an answer to this question when it is already answered by 4 different people.
â€“Â Rab
9 mins ago

OP meant that he thought that even obj2 is not used in anon class it still holds reference to it (which is false btw). Its not about final or not declarations.
â€“Â Antoniossss
9 mins ago

I answered base on title, obj2 in op post has no outside reference as long as Outer class is not instantiated
â€“Â Nertan Lucian
6 mins ago

You are missing the point and if you answered base on title, it is still off topic IMHO.
â€“Â Antoniossss
5 mins ago

add a commentÂ |Â

up vote
-2
down vote

This code displays 10, it's unaffected by garbage collector:

public class HelloWorld

 public static void main(String args)
 Outer q = new Outer();

 System.gc();
 System.runFinalization();

 q.method1().ok(4,1);



 

 interface Ok
 
 public void ok(int a, int b);
 


class Outer 
 private final int obj1 = 5;
 public Ok method1() 

 Ok justDoIt = new Ok()
 public void ok(int a, int b)
 
 System.out.println(obj1+a+b);
 


 ;

 return justDoIt;

To be honest I don't exactly understand your question.

But, a final variable or a "non-final" variable for GC are the same things. The only restriction is that when you try to set it again you are blocked.

Think of a final variable this way:

public class HelloWorld

 public static void main(String args)
 Final<Integer> q = new Final();
 q.set(5);
 System.out.println(q.get());

 q.set(10); // ERROR

 




class Final <T>

 private T variable;
 private Boolean setted=false;

 public void set(T value) throws Error
 if(setted) 
 throw new Error();
 

 variable=value;
 setted = true;
 

 public T get()return variable;

answered 10 mins ago

Nertan Lucian

9219

If you don't understand the OP why would you post an answer to this question when it is already answered by 4 different people.
â€“Â Rab
9 mins ago

OP meant that he thought that even obj2 is not used in anon class it still holds reference to it (which is false btw). Its not about final or not declarations.
â€“Â Antoniossss
9 mins ago

I answered base on title, obj2 in op post has no outside reference as long as Outer class is not instantiated
â€“Â Nertan Lucian
6 mins ago

You are missing the point and if you answered base on title, it is still off topic IMHO.
â€“Â Antoniossss
5 mins ago

add a commentÂ |Â

up vote
-2
down vote

This code displays 10, it's unaffected by garbage collector:

public class HelloWorld

 public static void main(String args)
 Outer q = new Outer();

 System.gc();
 System.runFinalization();

 q.method1().ok(4,1);



 

 interface Ok
 
 public void ok(int a, int b);
 


class Outer 
 private final int obj1 = 5;
 public Ok method1() 

 Ok justDoIt = new Ok()
 public void ok(int a, int b)
 
 System.out.println(obj1+a+b);
 


 ;

 return justDoIt;

To be honest I don't exactly understand your question.

But, a final variable or a "non-final" variable for GC are the same things. The only restriction is that when you try to set it again you are blocked.

Think of a final variable this way:

public class HelloWorld

 public static void main(String args)
 Final<Integer> q = new Final();
 q.set(5);
 System.out.println(q.get());

 q.set(10); // ERROR

 




class Final <T>

 private T variable;
 private Boolean setted=false;

 public void set(T value) throws Error
 if(setted) 
 throw new Error();
 

 variable=value;
 setted = true;
 

 public T get()return variable;

answered 10 mins ago

Nertan Lucian

9219

This code displays 10, it's unaffected by garbage collector:

public class HelloWorld

 public static void main(String args)
 Outer q = new Outer();

 System.gc();
 System.runFinalization();

 q.method1().ok(4,1);



 

 interface Ok
 
 public void ok(int a, int b);
 


class Outer 
 private final int obj1 = 5;
 public Ok method1() 

 Ok justDoIt = new Ok()
 public void ok(int a, int b)
 
 System.out.println(obj1+a+b);
 


 ;

 return justDoIt;

To be honest I don't exactly understand your question.

But, a final variable or a "non-final" variable for GC are the same things. The only restriction is that when you try to set it again you are blocked.

Think of a final variable this way:

public class HelloWorld

 public static void main(String args)
 Final<Integer> q = new Final();
 q.set(5);
 System.out.println(q.get());

 q.set(10); // ERROR

 




class Final <T>

 private T variable;
 private Boolean setted=false;

 public void set(T value) throws Error
 if(setted) 
 throw new Error();
 

 variable=value;
 setted = true;
 

 public T get()return variable;

answered 10 mins ago

Nertan Lucian

9219

answered 10 mins ago

Nertan Lucian

9219

answered 10 mins ago

Nertan Lucian

9219

answered 10 mins ago

Nertan Lucian

9219

If you don't understand the OP why would you post an answer to this question when it is already answered by 4 different people.
â€“Â Rab
9 mins ago

OP meant that he thought that even obj2 is not used in anon class it still holds reference to it (which is false btw). Its not about final or not declarations.
â€“Â Antoniossss
9 mins ago

I answered base on title, obj2 in op post has no outside reference as long as Outer class is not instantiated
â€“Â Nertan Lucian
6 mins ago

You are missing the point and if you answered base on title, it is still off topic IMHO.
â€“Â Antoniossss
5 mins ago

add a commentÂ |Â

If you don't understand the OP why would you post an answer to this question when it is already answered by 4 different people.
â€“Â Rab
9 mins ago

OP meant that he thought that even obj2 is not used in anon class it still holds reference to it (which is false btw). Its not about final or not declarations.
â€“Â Antoniossss
9 mins ago

I answered base on title, obj2 in op post has no outside reference as long as Outer class is not instantiated
â€“Â Nertan Lucian
6 mins ago

You are missing the point and if you answered base on title, it is still off topic IMHO.
â€“Â Antoniossss
5 mins ago

If you don't understand the OP why would you post an answer to this question when it is already answered by 4 different people.
â€“Â Rab
9 mins ago

OP meant that he thought that even obj2 is not used in anon class it still holds reference to it (which is false btw). Its not about final or not declarations.
â€“Â Antoniossss
9 mins ago

I answered base on title, obj2 in op post has no outside reference as long as Outer class is not instantiated
â€“Â Nertan Lucian
6 mins ago

You are missing the point and if you answered base on title, it is still off topic IMHO.
â€“Â Antoniossss
5 mins ago

add a commentÂ |Â

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