Java-Java中this的疑惑

Question

public class Test05 {
    public static void main(String[] args) {
        Father obj = new Son();
        System.out.println(obj.name);
    }
}

class Father{
    public String name = "父类字段";
    Father(){
        System.out.println(this);
        System.out.println(this.name);
    }
}

class Son extends Father{
    public String name = "子类字段";
}

Answer 1

JLS8:

https://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#jls-8.1.6

If the class declares a field with a certain name, then the declaration of that field is said to hide any and all accessible declarations of fields with the same name in superclasses, and superinterfaces of the class.
In this respect, hiding of fields differs from hiding of methods (§8.4.8.3), for there is no distinction drawn between static and non-static fields in field hiding whereas a distinction is drawn between static and non-static methods in method hiding.
A hidden field can be accessed by using a qualified name (§6.5.6.2) if it is static, or by using a field access expression that contains the keyword super (§15.11.2) or a cast to a superclass type.

就是说, 父类的 同名字段被隐藏了, 可以通过 cast to a superclass type 来调用此字段.

 public class Test05 {
public static void main(String[] args) {
Child obj = new Child();
System.out.println(obj.name);
System.out.println(((Father)obj).name);
}
}

class Father {
public String name = "Father";
}

class Child extends Father {
public String name = "Child";
}

结果:
Child
Father

字节码:

  public static void main(java.lang.String[] args);
0 new Child [16]
3 dup
4 invokespecial Child() [18]
7 astore_1 [obj]
8 getstatic java.lang.System.out : java.io.PrintStream [19]
11 aload_1 [obj]
12 getfield Child.name : java.lang.String [25]
15 invokevirtual java.io.PrintStream.println(java.lang.String) : void [29]
18 getstatic java.lang.System.out : java.io.PrintStream [19]
21 aload_1 [obj]
22 getfield Father.name : java.lang.String [35]
25 invokevirtual java.io.PrintStream.println(java.lang.String) : void [29]
28 return