java中函数传值与引用问题

Posted 2021-02-07 GISer-Li

从C++转java，在使用函数传对象时，碰到一点问题，今天特意验证了一下：

public class App 
{
    public static void doubleTest(double d) {
        d=8.0;
        System.out.println( "[INNER doubleTest]double:"+d);
    }
    public static void DoubleTest(Double dd) {
        dd=8.0;
        System.out.println( "[INNER DoubleTest]Double:"+dd);
    }
    public static void ObjectTest(ObjectChange obj) {
        obj = new ObjectChange(5);
        System.out.println( "[INNER ObjectTest]Object:"+obj.getTT());
        obj.setTT(8);
        System.out.println( "[INNER ObjectTest]Object:"+obj.getTT());
    }
    public static void ObjectChangeTest(ObjectChange obj) {
        obj.setTT(8);
        System.out.println( "[INNER ObjectChangeTest]Object:"+obj.getTT());
        obj = new ObjectChange(5);
        System.out.println( "[INNER ObjectChangeTest]Object:"+obj.getTT());
        obj.setTT(6);
        System.out.println( "[INNER ObjectChangeTest]Object:"+obj.getTT());
    }
    
    public static void main( String[] args )
    {
        System.out.println( "Source:" );
        double d1=1;
        Double d2=2.0;
        ObjectChange obj1 = new ObjectChange(1);
        System.out.println( "double:"+d1+"    Double:"+d2 +"    Object:"+ obj1.getTT());        

        System.out.println( "After:" );
        doubleTest(d1);
        DoubleTest(d2);
        ObjectTest(obj1);
        System.out.println( "double:"+d1+"    Double:"+d2 +"    Object:"+ obj1.getTT());
        ObjectChangeTest(obj1);
        System.out.println( "Object:"+ obj1.getTT());
    }
}

程序输出结果：

总结：

obj在函数体内作为临时变量，可读取对象内容，采用“=”（赋值运算符）改变的是临时对象的内容，赋值后，再操作的也是临时对象的内容；

只有在赋值前调用对象的成员方法（setTT()）才能真正改变obj对象的内容；