constructor have include a void return type?

for example

class A {

void A() //where A is constructor and which return type is void,it is valid

{

}

public static void main(string arg[])

A a = new A();

}

---

A constructor does not have a result / return type.

If you add a result / return type to a "constructor" you turn it into a method whose name is the same as the class name. Then new won't be able to use it, and any this(...) or super(...) call in the method will be a syntax error.

---

For your example, you won't actually get an error. That is because Java will add a default no-args constructor for A ... because you haven't actually defined any constructors. The new in your example will actually be using the default constructor ....

If you changed your code to this:

class A {
    void A() { System.err.println("hello"); }

    public static void main(string arg[]) {
        A a = new A();
    }
}

and compiled and ran it, you should see that it DOES NOT give you any output. Remove the void and you will see output.

---

so here A() work as a method

It >>is<< a method. But it is not "working". As my version of your example shows ... the method is not being called at all.

---

You are confused why your code compiles. It's because A() is not actually a constructor but a method (that unfortunately has the same name as the class). The class A has an implicit default constructor which is used by main . The method A() is not used.

As others have pointed out, constructors do not have a return type.

链接地址: http://www.djcxy.com/p/49634.html

上一篇: setInterval替代

下一篇: 构造函数有一个void返回类型？