Java strange syntax - (Anonymous sub-class)

Question

I have come across below strange syntax, I have never seen such snippet, it is not necessity but curious to understand it

new Object() {
    void hi(String in) {
        System.out.println(in);
    }
}.hi("strange");

Above code gives output as strange

thanks

Answer 1

You've created an anonymous sub-class of Object , which introduces a method, called hi , after which you invoke this method with parameter "strange" .

Let's suppose you had:

class NamedClass extends Object {
    void hi(String in) { System.out.println(in); }
}

NamedClass instance = new NamedClass();
instance.hi("strange");

If this class was needed at exactly one place, there's no real need of being named and so on - by making it an anonymous class, you get rid of its name, the class gets defined and instantiated and the hi method invoked immediately within a single expression.

Answer 2

这是完全正常的，被称为匿名类，它经常使用，如果您想将对象引用传递给函数，则可以使用匿名类或使用回调来实现，现在.hi结尾是有效的，因为您只是使用new运算符实例化了Object类型的对象，并且对其具有引用，因此这才起作用。

Answer 3

You've created an annonymous sub-class of Object and then invoke the method. Four types of anonymous inner class exists :-

1)Inner class,
2)Static nested classes
3)Method local inner classes
4)Anonymous inner classes

In Annonymous inner classes,you can define,instantiate and use that inner object then and there