java - 是否可以在您在 java 中创建实例的同一行中调用方法

Question

class BooleanWrap{
    boolean b = new Boolean("true").booleanValue(); 
}

当我尝试对下面的代码执行相同操作时，它不起作用：

class TestCode  {
    public static void main(String[] ar)  {
        TestCode tc = new TestCode().go();
    }

    void go() {
        //some code
    }
}

编译错误：

TestBox.java:6: 错误：不兼容的类型 TestBox t = new TestBox().go();

当我将方法的返回类型go()从更改void为类类型时，我不再收到错误消息。

class TestCode2 {
    public static void main(String[] ar) {
        TestCode2 tc2 = new TestCode2().go();
    }

    TestCode2 go() {
        //some code
    }
}

我刚刚在上面的代码中创建的对象（由 引用tc2）会发生什么？会被抛弃吗？

Answer 1

This should work just fine:

class TestCode{
    public static void main(String[] ar){
        new TestCode().go();
    }

    void go() {
        System.out.println("Hello World");
    }
 }

Edit: Additional info

This way you can't save the created instance. It will get destroyed right away in the next garbage collection. So normally, to avoid this unneccessary creation and destruction a static method would be used if the instance itself is not needed.

class TestCode{
    public static void main(String[] ar){
        TestCode.go();
    }

    static void go() {
        System.out.println("Hello World");
    }
 }

Answer 2

TestCode tc = new TestCode().go()仅当go()方法返回 a时才有效TestCode，因为您将其分配给TestCode类型的变量。

在 的情况下TestCode2 tc2 = new TestCode2().go();，如果该go()方法返回对不同实例的引用TestCode2（即不是您调用的那个go()），则原始实例将不会在任何地方被引用，并且有资格进行垃圾回收。换句话说，tc2将引用由返回的实例go()，它不必与在 main 方法中创建的实例相同new TestCode2()。

Answer 3

As Eran said, the method go() returns nothing, and you're trying to assing that nothing to a variable, your method needs to return something, a TestCode object in this case