JLabel and JTextField string comparison

Question

When I use JLabel string comparison with == works fine

private JLabel someJLabel = new JLabel("some text");
...
System.out.println (someJLabel.getText() == "some text"); // returns true

but when I use JTextField

private JTextField someJTextField = new JTextField("some text");
...
System.out.println (someJTextField.getText() == "some text"); // returns false

I know that if I used someJTextField.getText().equals("some text"); it would work fine.

So why it works with JLabel but not JTextField

EDIT: yes I know that I should use .equals with string, I have read this article http://javatechniques.com/blog/string-equality-and-interning/ but it's known already that I will use "some text" so it could refer to same string object

score 3 · Answer 1 · edited May 23 '17 at 12:12

3

It's not related to JTextField and JLabel.

JVM uses String pool internally and sometimes == operator works because different strings (in your case "some text") points to the same string in pool. Look at question here

Never compare strings with == !!!

edited May 23 '17 at 12:12

Community

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answered Dec 07 '11 at 16:26

korifey

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I guess because label has simple string as it's model (data) inside, but JTextField has Document. So when you creates JTextField("some text") it transform "some text" into it's internal document representation (may be char array or something like this) and when you call someJTextField.getText() it invokes new String(char[]) constructor - so string identity is different from original (it points to another place in heap) – korifey Dec 07 '11 at 17:32

score 1 · Accepted Answer · answered Dec 07 '11 at 16:29

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JTextField internally copies the string to its modifiable document object to support editing so you don't get back the same string in getText().

answered Dec 07 '11 at 16:29

Ashwinee K Jha

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I mean in JLabel setText(t) is like this.text = t; while in JTextField it is like this.getDocument().insertText(t); So t is not preserved. If you take a look at the implementation of setText() method in these classes in source of jdk this will become more obvious. – Ashwinee K Jha Dec 07 '11 at 17:19

score 0 · Answer 3 · edited Mar 18 '15 at 08:59

0

There is a bit difference in == operator and.equals method. == operator compares two objects while .equals method compare values in two object.

In your case you are comparing two different object although both may be holding same values. In your case you may use .equals method .This will definitely help!

edited Mar 18 '15 at 08:59

talegna

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answered Mar 18 '15 at 08:35

Gandalf the white

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score 0 · Answer 4 · edited Dec 07 '11 at 16:56

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Compare Strings with .equals(Object obj)

== should mostly be used with only primitive objects.

edited Dec 07 '11 at 16:56

Kai

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answered Dec 07 '11 at 16:33

Matt

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JLabel and JTextField string comparison

4 Answers4