CODEWITHSUNDEEP
java
shai
shai

Reputation: 109

What are curly braces after function call for?

In the following code, what does Type type mean, and what are the curly brackets are used for?

Type type = new TypeToken<List<String>>(){}.getType();
List<String> list = converter.fromJson(jsonStringArray, type );

Upvotes: 10

Views: 2408

Answers (3)

Luca Mastrostefano
Luca Mastrostefano

Reputation: 3271

The curly brackets are the anonymous class constructor and are use after a constructor call. Inside you can override or create a method.

Example:

    private static class Foo {

    public int baz() {
        return 0;
    }
}

public static void main(final String[] args) {
    final Foo foo = new Foo() {
        @Override
        public int baz() {
            return 1;
        }
    };

    System.out.println(foo.baz());
}

Output:

1

Upvotes: 1

adarshr
adarshr

Reputation: 62583

Type is a class.

new TypeToken<List<String>>() {
}.getType();

Is creating an anonymous inner class and invoking getType() on the object created.

Upvotes: 8

Joshua Taylor
Joshua Taylor

Reputation: 85823

That's not after a function call, but after a constructor call. The line

Type type = new TypeToken<List<String>>(){}.getType();

is creating an instance of an anonymous subclass of TypeToken, and then calling its getType() method. You could do the same in two lines:

TypeToken<List<String>> typeToken = new TypeToken<List<String>>(){};
Type type = typeToken.getType();

The Java Tutorial Anonymous Subclasses has more examples of this. This is a somewhat peculiar usage, since no methods are being overridden, and no instance initialization block is being used. (See Initializing Fields for more about instance initialization blocks.)

Upvotes: 8

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