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Double brace initialisation

Page history last edited by Manuel Kueblboeck 14 years, 7 months ago

This is a Java trick which involves creating an anonymous class with an initialiser block, eg.

new Object() {{
    // Initialisation stuff here
}};

It can enhance the readability of collection creation:

List<Integer> list = new ArrayList<Integer>() {{

add(1);

add(2);

add(3);

add(4);

add(5);

}};

 

Map<Integer, String> map = new HashMap<Integer, String>() {{

put(1, "one");

put(2, "two");

put(3, "three");

put(4, "four");

put(5, "five");

}};

But can also be useful in GUI programming:

JFrame frame = new JFrame() {{

setDefaultCloseOperation(EXIT_ON_CLOSE);

add(new JLabel("Hello, World!"));

pack();

}};

 

Be careful when using this, however, because any object created using double brace initialisation belongs to an anonymous subclass, not the original class. 

I found this gem at refactory.org.

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