新Test（）和新Test（）{}之间的区别 [英] Difference between new Test() and new Test() { }

问题描述

这两种实例化类的新对象的方法有何不同，如下所示：

What is the difference between these two ways of instantiating new objects of a class as follows:

Test t1=new Test();
Test t2=new Test(){ };

当我尝试以下代码时，我可以看到两个对象都可以访问方法 foo（），但是t2无法访问变量x （变量x 不能待解决）：

When I tried the following code, I could see that both objects could access the method foo(), but t2 cannot access the variable x (variable x cannot be resolved):

public class Test
{ 
    int x=0;
    public void foo(){ }

    public static void main (String args[])
    {
        Test t1=new Test();
        Test t2=new Test(){ };
        t1.x=10;
        t2.x=20;
        t1.foo();
        t2.foo();
        System.out.println(t1.x+" "t2.x);
    }
}

推荐答案

测试t2 = new Test（）; 将创建Test类的对象。

Test t2=new Test(); will create the object of Test class.

但是测试t2 = new Test（）{}; 将创建一个测试子类的对象（即匿名在这种情况下的内部类）。

But Test t2=new Test(){ }; will create a object of subclass of test (i.e. anonymous inner class in this case).

你可以为那里的任何方法提供实现，如

you can provide implementation for any method over there like

Test t2=new Test(){ 
public void foo(){ System.out.println("This is foo");}
};

这样当 foo（）方法调用时从对象 t2 它将打印这是foo 。

so that when foo() method called from object t2 it will print This is foo.

添加

代码中的编译时错误是由于缺少连接操作符

Compile time error in your code is due to missing concatination operator

System.out.println(t1.x+" "+t2.x);
                          ###

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