How check if the lists in a list are not empty

up vote
7
down vote

favorite

I have a list of lists in Java. Here is the code:

List<List<Integer>> myList = new ArrayList<>();
myList.add(new ArrayList<Integer>());
myList.add(new ArrayList<Integer>());
myList.add(new ArrayList<Integer>());

myList.get(0).add(1);
myList.get(0).add(2);
myList.get(0).add(3);
myList.get(1).add(4);
myList.get(1).add(5);
myList.get(1).add(6);
myList.get(2).add(7);
myList.get(2).add(8);
myList.get(2).add(9);

Now in a part of my code I want to check if all three lists that are located in list are not empty. Should I check each of these lists one by one like if (myList.get(0) != null && !myList.get(0).isEmpty()) do something or is there a better and shorter way to do instead of checking one by one?

edited 37 mins ago

asked 46 mins ago

helen

173111

add a commentÂ |Â

up vote
7
down vote

favorite

I have a list of lists in Java. Here is the code:

List<List<Integer>> myList = new ArrayList<>();
myList.add(new ArrayList<Integer>());
myList.add(new ArrayList<Integer>());
myList.add(new ArrayList<Integer>());

myList.get(0).add(1);
myList.get(0).add(2);
myList.get(0).add(3);
myList.get(1).add(4);
myList.get(1).add(5);
myList.get(1).add(6);
myList.get(2).add(7);
myList.get(2).add(8);
myList.get(2).add(9);

edited 37 mins ago

asked 46 mins ago

helen

173111

add a commentÂ |Â

up vote
7
down vote

favorite

I have a list of lists in Java. Here is the code:

List<List<Integer>> myList = new ArrayList<>();
myList.add(new ArrayList<Integer>());
myList.add(new ArrayList<Integer>());
myList.add(new ArrayList<Integer>());

myList.get(0).add(1);
myList.get(0).add(2);
myList.get(0).add(3);
myList.get(1).add(4);
myList.get(1).add(5);
myList.get(1).add(6);
myList.get(2).add(7);
myList.get(2).add(8);
myList.get(2).add(9);

edited 37 mins ago

asked 46 mins ago

helen

173111

I have a list of lists in Java. Here is the code:

List<List<Integer>> myList = new ArrayList<>();
myList.add(new ArrayList<Integer>());
myList.add(new ArrayList<Integer>());
myList.add(new ArrayList<Integer>());

myList.get(0).add(1);
myList.get(0).add(2);
myList.get(0).add(3);
myList.get(1).add(4);
myList.get(1).add(5);
myList.get(1).add(6);
myList.get(2).add(7);
myList.get(2).add(8);
myList.get(2).add(9);

java list

edited 37 mins ago

asked 46 mins ago

helen

173111

edited 37 mins ago

asked 46 mins ago

helen

173111

edited 37 mins ago

asked 46 mins ago

helen

173111

asked 46 mins ago

helen

173111

asked 46 mins ago

helen

173111

add a commentÂ |Â

5 Answers
5

active

oldest

votes

up vote
7
down vote

You can use stream api for this, but also a plain loop too:

 boolean allNonEmptyOrNull = myList.stream()
 .allMatch(x -> x != null && !x.isEmpty());

Or you can check if null is contained or an an empty List for example, via:

System.out.println(myList.contains(null) || myList.contains(Collections.<Integer> emptyList()));

But this last option will break with java-9 immutable collections, for example:

List.of(1, 2, 3).contains(null);

will throw a NullPointerException

edited 31 mins ago

answered 45 mins ago

Eugene

63.3k987146

Are you sure contains(null) will throw an error?
â€“Â shmosel
13 mins ago

@shmosel yes, I do
â€“Â Eugene
10 mins ago

That's very surprising. Awful design decision, if you ask me.
â€“Â shmosel
51 secs ago

add a commentÂ |Â

up vote
3
down vote

Just check your collection not contains empty list

if (!L.contains(Collections.EMPTY_LIST)) do something

or empty and null check (be care with NullPointerException !!!)

if (!L.contains(Collections.EMPTY_LIST) && !L.contains(null)) do something

edited 6 mins ago

answered 41 mins ago

Mark

1542

New contributor

almost correct, you have to check against null too
â€“Â Eugene
33 mins ago

Q was "are not empty". But check for null not a problem too.
â€“Â Mark
27 mins ago

you are right, but the code in the question was myList.get(0) != null...
â€“Â Eugene
26 mins ago

and now that you have written it - it might fail if the main list is an immutable list, like java-9 has (did not downvote btw)
â€“Â Eugene
22 mins ago

you are right, thank!
â€“Â Mark
15 mins ago

add a commentÂ |Â

up vote
1
down vote

int temp = 0;
 for(int i=0;i<L.size();i++) 
 if (L.get(i).isEmpty()) 
 temp++;
 
 
 if (temp == L.size()) 
 //do what you want, all the lists inside L are empty

This is all i can think of right now :)

answered 23 mins ago

Ibtihaj Uddin

286

add a commentÂ |Â

up vote
1
down vote

You can do something like this:

boolean isEmpty = false;
for(list in myList) 

if(!isEmpty) // do your thing;

edited 23 mins ago

answered 33 mins ago

Pritam Banerjee

10.1k64262

Why the downvote?
â€“Â Pritam Banerjee
25 mins ago

add a commentÂ |Â

up vote
1
down vote

Using Java 7 and below this is the classical way to approach that:

for (List<Integer> list : myList) 
 if (list != null && !list.isEmpty()) 
 // do something with not empty list

With Java 8 and above you can use forEach:

myList.forEach(list -> 
 if (list != null && !list.isEmpty()) 
 // do something with not empty list
 
);

or, as already mentioned by Eugene add stream API touch to it:

myList.stream()
 .filter(list -> (list != null && !list.isEmpty()))
 .forEach(list -> 
 // do something with not empty list
 );

Note: all these 3 examples imply that you have initialized myList variable and it is not null, otherwise NullPointerException will be thrown in all snippets above.

Standard JDK does not have a quick way to check that collection is not null and not empty. But if you are using Apache commons-collections library, they offer such a method: CollectionUtils.isNotEmpty(). However, I would not recommend, to add this dependency into your project just for the sake of this single function.

edited 8 mins ago

answered 24 mins ago

Vladimir L.

692615

add a commentÂ |Â

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5 Answers
5

active

oldest

votes

5 Answers
5

active

oldest

votes

up vote
7
down vote

You can use stream api for this, but also a plain loop too:

 boolean allNonEmptyOrNull = myList.stream()
 .allMatch(x -> x != null && !x.isEmpty());

Or you can check if null is contained or an an empty List for example, via:

System.out.println(myList.contains(null) || myList.contains(Collections.<Integer> emptyList()));

But this last option will break with java-9 immutable collections, for example:

List.of(1, 2, 3).contains(null);

will throw a NullPointerException

edited 31 mins ago

answered 45 mins ago

Eugene

63.3k987146

Are you sure contains(null) will throw an error?
â€“Â shmosel
13 mins ago

@shmosel yes, I do
â€“Â Eugene
10 mins ago

That's very surprising. Awful design decision, if you ask me.
â€“Â shmosel
51 secs ago

add a commentÂ |Â

up vote
7
down vote

You can use stream api for this, but also a plain loop too:

 boolean allNonEmptyOrNull = myList.stream()
 .allMatch(x -> x != null && !x.isEmpty());

Or you can check if null is contained or an an empty List for example, via:

System.out.println(myList.contains(null) || myList.contains(Collections.<Integer> emptyList()));

But this last option will break with java-9 immutable collections, for example:

List.of(1, 2, 3).contains(null);

will throw a NullPointerException

edited 31 mins ago

answered 45 mins ago

Eugene

63.3k987146

Are you sure contains(null) will throw an error?
â€“Â shmosel
13 mins ago

@shmosel yes, I do
â€“Â Eugene
10 mins ago

That's very surprising. Awful design decision, if you ask me.
â€“Â shmosel
51 secs ago

add a commentÂ |Â

up vote
7
down vote

You can use stream api for this, but also a plain loop too:

 boolean allNonEmptyOrNull = myList.stream()
 .allMatch(x -> x != null && !x.isEmpty());

Or you can check if null is contained or an an empty List for example, via:

System.out.println(myList.contains(null) || myList.contains(Collections.<Integer> emptyList()));

But this last option will break with java-9 immutable collections, for example:

List.of(1, 2, 3).contains(null);

will throw a NullPointerException

edited 31 mins ago

answered 45 mins ago

Eugene

63.3k987146

You can use stream api for this, but also a plain loop too:

 boolean allNonEmptyOrNull = myList.stream()
 .allMatch(x -> x != null && !x.isEmpty());

Or you can check if null is contained or an an empty List for example, via:

System.out.println(myList.contains(null) || myList.contains(Collections.<Integer> emptyList()));

But this last option will break with java-9 immutable collections, for example:

List.of(1, 2, 3).contains(null);

will throw a NullPointerException

edited 31 mins ago

answered 45 mins ago

Eugene

63.3k987146

edited 31 mins ago

answered 45 mins ago

Eugene

63.3k987146

answered 45 mins ago

Eugene

63.3k987146

answered 45 mins ago

Eugene

63.3k987146

Are you sure contains(null) will throw an error?
â€“Â shmosel
13 mins ago

@shmosel yes, I do
â€“Â Eugene
10 mins ago

That's very surprising. Awful design decision, if you ask me.
â€“Â shmosel
51 secs ago

add a commentÂ |Â

Are you sure contains(null) will throw an error?
â€“Â shmosel
13 mins ago

@shmosel yes, I do
â€“Â Eugene
10 mins ago

That's very surprising. Awful design decision, if you ask me.
â€“Â shmosel
51 secs ago

Are you sure contains(null) will throw an error?
â€“Â shmosel
13 mins ago

@shmosel yes, I do
â€“Â Eugene
10 mins ago

That's very surprising. Awful design decision, if you ask me.
â€“Â shmosel
51 secs ago

add a commentÂ |Â

up vote
3
down vote

Just check your collection not contains empty list

if (!L.contains(Collections.EMPTY_LIST)) do something

or empty and null check (be care with NullPointerException !!!)

if (!L.contains(Collections.EMPTY_LIST) && !L.contains(null)) do something

edited 6 mins ago

answered 41 mins ago

Mark

1542

New contributor

almost correct, you have to check against null too
â€“Â Eugene
33 mins ago

Q was "are not empty". But check for null not a problem too.
â€“Â Mark
27 mins ago

you are right, but the code in the question was myList.get(0) != null...
â€“Â Eugene
26 mins ago

and now that you have written it - it might fail if the main list is an immutable list, like java-9 has (did not downvote btw)
â€“Â Eugene
22 mins ago

you are right, thank!
â€“Â Mark
15 mins ago

add a commentÂ |Â

up vote
3
down vote

Just check your collection not contains empty list

if (!L.contains(Collections.EMPTY_LIST)) do something

or empty and null check (be care with NullPointerException !!!)

if (!L.contains(Collections.EMPTY_LIST) && !L.contains(null)) do something

edited 6 mins ago

answered 41 mins ago

Mark

1542

New contributor

almost correct, you have to check against null too
â€“Â Eugene
33 mins ago

Q was "are not empty". But check for null not a problem too.
â€“Â Mark
27 mins ago

you are right, but the code in the question was myList.get(0) != null...
â€“Â Eugene
26 mins ago

and now that you have written it - it might fail if the main list is an immutable list, like java-9 has (did not downvote btw)
â€“Â Eugene
22 mins ago

you are right, thank!
â€“Â Mark
15 mins ago

add a commentÂ |Â

up vote
3
down vote

Just check your collection not contains empty list

if (!L.contains(Collections.EMPTY_LIST)) do something

or empty and null check (be care with NullPointerException !!!)

if (!L.contains(Collections.EMPTY_LIST) && !L.contains(null)) do something

edited 6 mins ago

answered 41 mins ago

Mark

1542

New contributor

Just check your collection not contains empty list

if (!L.contains(Collections.EMPTY_LIST)) do something

or empty and null check (be care with NullPointerException !!!)

if (!L.contains(Collections.EMPTY_LIST) && !L.contains(null)) do something

edited 6 mins ago

answered 41 mins ago

Mark

1542

New contributor

edited 6 mins ago

answered 41 mins ago

Mark

1542

New contributor

answered 41 mins ago

Mark

1542

answered 41 mins ago

Mark

1542

New contributor

Mark is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

almost correct, you have to check against null too
â€“Â Eugene
33 mins ago

Q was "are not empty". But check for null not a problem too.
â€“Â Mark
27 mins ago

you are right, but the code in the question was myList.get(0) != null...
â€“Â Eugene
26 mins ago

and now that you have written it - it might fail if the main list is an immutable list, like java-9 has (did not downvote btw)
â€“Â Eugene
22 mins ago

you are right, thank!
â€“Â Mark
15 mins ago

add a commentÂ |Â

almost correct, you have to check against null too
â€“Â Eugene
33 mins ago

Q was "are not empty". But check for null not a problem too.
â€“Â Mark
27 mins ago

you are right, but the code in the question was myList.get(0) != null...
â€“Â Eugene
26 mins ago

and now that you have written it - it might fail if the main list is an immutable list, like java-9 has (did not downvote btw)
â€“Â Eugene
22 mins ago

you are right, thank!
â€“Â Mark
15 mins ago

almost correct, you have to check against null too
â€“Â Eugene
33 mins ago

Q was "are not empty". But check for null not a problem too.
â€“Â Mark
27 mins ago

you are right, but the code in the question was myList.get(0) != null...
â€“Â Eugene
26 mins ago

and now that you have written it - it might fail if the main list is an immutable list, like java-9 has (did not downvote btw)
â€“Â Eugene
22 mins ago

you are right, thank!
â€“Â Mark
15 mins ago

add a commentÂ |Â

up vote
1
down vote

int temp = 0;
 for(int i=0;i<L.size();i++) 
 if (L.get(i).isEmpty()) 
 temp++;
 
 
 if (temp == L.size()) 
 //do what you want, all the lists inside L are empty

This is all i can think of right now :)

answered 23 mins ago

Ibtihaj Uddin

286

add a commentÂ |Â

up vote
1
down vote

int temp = 0;
 for(int i=0;i<L.size();i++) 
 if (L.get(i).isEmpty()) 
 temp++;
 
 
 if (temp == L.size()) 
 //do what you want, all the lists inside L are empty

This is all i can think of right now :)

answered 23 mins ago

Ibtihaj Uddin

286

add a commentÂ |Â

up vote
1
down vote

int temp = 0;
 for(int i=0;i<L.size();i++) 
 if (L.get(i).isEmpty()) 
 temp++;
 
 
 if (temp == L.size()) 
 //do what you want, all the lists inside L are empty

This is all i can think of right now :)

answered 23 mins ago

Ibtihaj Uddin

286

int temp = 0;
 for(int i=0;i<L.size();i++) 
 if (L.get(i).isEmpty()) 
 temp++;
 
 
 if (temp == L.size()) 
 //do what you want, all the lists inside L are empty

This is all i can think of right now :)

answered 23 mins ago

Ibtihaj Uddin

286

answered 23 mins ago

Ibtihaj Uddin

286

answered 23 mins ago

Ibtihaj Uddin

286

answered 23 mins ago

Ibtihaj Uddin

286

add a commentÂ |Â

up vote
1
down vote

You can do something like this:

boolean isEmpty = false;
for(list in myList) 

if(!isEmpty) // do your thing;

edited 23 mins ago

answered 33 mins ago

Pritam Banerjee

10.1k64262

Why the downvote?
â€“Â Pritam Banerjee
25 mins ago

add a commentÂ |Â

up vote
1
down vote

You can do something like this:

boolean isEmpty = false;
for(list in myList) 

if(!isEmpty) // do your thing;

edited 23 mins ago

answered 33 mins ago

Pritam Banerjee

10.1k64262

Why the downvote?
â€“Â Pritam Banerjee
25 mins ago

add a commentÂ |Â

up vote
1
down vote

You can do something like this:

boolean isEmpty = false;
for(list in myList) 

if(!isEmpty) // do your thing;

edited 23 mins ago

answered 33 mins ago

Pritam Banerjee

10.1k64262

You can do something like this:

boolean isEmpty = false;
for(list in myList) 

if(!isEmpty) // do your thing;

edited 23 mins ago

answered 33 mins ago

Pritam Banerjee

10.1k64262

edited 23 mins ago

answered 33 mins ago

Pritam Banerjee

10.1k64262

answered 33 mins ago

Pritam Banerjee

10.1k64262

answered 33 mins ago

Pritam Banerjee

10.1k64262

Why the downvote?
â€“Â Pritam Banerjee
25 mins ago

add a commentÂ |Â

Why the downvote?
â€“Â Pritam Banerjee
25 mins ago

Why the downvote?
â€“Â Pritam Banerjee
25 mins ago

add a commentÂ |Â

up vote
1
down vote

Using Java 7 and below this is the classical way to approach that:

for (List<Integer> list : myList) 
 if (list != null && !list.isEmpty()) 
 // do something with not empty list

With Java 8 and above you can use forEach:

myList.forEach(list -> 
 if (list != null && !list.isEmpty()) 
 // do something with not empty list
 
);

or, as already mentioned by Eugene add stream API touch to it:

myList.stream()
 .filter(list -> (list != null && !list.isEmpty()))
 .forEach(list -> 
 // do something with not empty list
 );

Note: all these 3 examples imply that you have initialized myList variable and it is not null, otherwise NullPointerException will be thrown in all snippets above.

edited 8 mins ago

answered 24 mins ago

Vladimir L.

692615

add a commentÂ |Â

up vote
1
down vote

Using Java 7 and below this is the classical way to approach that:

for (List<Integer> list : myList) 
 if (list != null && !list.isEmpty()) 
 // do something with not empty list

With Java 8 and above you can use forEach:

myList.forEach(list -> 
 if (list != null && !list.isEmpty()) 
 // do something with not empty list
 
);

or, as already mentioned by Eugene add stream API touch to it:

myList.stream()
 .filter(list -> (list != null && !list.isEmpty()))
 .forEach(list -> 
 // do something with not empty list
 );

Note: all these 3 examples imply that you have initialized myList variable and it is not null, otherwise NullPointerException will be thrown in all snippets above.

edited 8 mins ago

answered 24 mins ago

Vladimir L.

692615

add a commentÂ |Â

up vote
1
down vote

Using Java 7 and below this is the classical way to approach that:

for (List<Integer> list : myList) 
 if (list != null && !list.isEmpty()) 
 // do something with not empty list

With Java 8 and above you can use forEach:

myList.forEach(list -> 
 if (list != null && !list.isEmpty()) 
 // do something with not empty list
 
);

or, as already mentioned by Eugene add stream API touch to it:

myList.stream()
 .filter(list -> (list != null && !list.isEmpty()))
 .forEach(list -> 
 // do something with not empty list
 );

Note: all these 3 examples imply that you have initialized myList variable and it is not null, otherwise NullPointerException will be thrown in all snippets above.

edited 8 mins ago

answered 24 mins ago

Vladimir L.

692615

Using Java 7 and below this is the classical way to approach that:

for (List<Integer> list : myList) 
 if (list != null && !list.isEmpty()) 
 // do something with not empty list

With Java 8 and above you can use forEach:

myList.forEach(list -> 
 if (list != null && !list.isEmpty()) 
 // do something with not empty list
 
);

or, as already mentioned by Eugene add stream API touch to it:

myList.stream()
 .filter(list -> (list != null && !list.isEmpty()))
 .forEach(list -> 
 // do something with not empty list
 );

Note: all these 3 examples imply that you have initialized myList variable and it is not null, otherwise NullPointerException will be thrown in all snippets above.

edited 8 mins ago

answered 24 mins ago

Vladimir L.

692615

edited 8 mins ago

answered 24 mins ago

Vladimir L.

692615

answered 24 mins ago

Vladimir L.

692615

answered 24 mins ago

Vladimir L.

692615

add a commentÂ |Â

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