Java 构造函数引用赋值与新创建的对象赋值

Question

I met in our project following code:

MyInterface var = MyClass::new;

Is there difference with

MyInterface var = new MyClass();

Lazy?

Answer 1

MyInterface var = new MyClass();

creates an instance of MyClass and assigns it to a variable of type MyInterface . This requires that MyClass implements MyInterface and have a no-arg constructor. The result is an instance of MyClass which implements MyInterface however it likes to.

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MyInterface var = MyClass::new;

attemps to implement MyInterface ad-hoc. This requires that MyInterface is a functional interface having a single abstract method. That single abstract method must have a return type assignable from MyClass and a parameter list matching one of MyClass ' constructors.

It is analog of:

MyInterface var = new MyInterface() {
    public MyClass anyMethodName() {
        return new MyClass();
    }
}

The result is an instance of MyInterface which will on invocations of its single abstract method create a new instance of MyClass passing all of its arguments to the constructor of MyClass .

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In other words, these two constructs have nothing in common.