How toString() overriding works

Question

I just learnt about the toString() method in object class and how to override it in other class.

class Box {
      public String toString(){
          return "class Box";
      }
}

class B {
    public static void main(String args[]){
        Box b1=new Box();
        System.out.println(b1); //case 1
        Box b2=b1; //case 2
    }
}

So my question is how does box object know to return the String in the toString() in class Box in case 1 and return the b1 object's address in case 2?

This doesn't really have to do with `toString()` overriding, but more with how `System.out.println(Object)` works. — Mark Rotteveel, Jan 24 '20 at 14:58

score 3 · Answer 1 · answered Jan 24 '20 at 14:37

3

The System.out.println method you are calling is the (Object) overload, not (String). PrintStream.println(Object) calls toString() on its argument (pedantry: directly or indirectly, unless the argument is null).

answered Jan 24 '20 at 14:37

Tom Hawtin - tackline

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score 2 · Answer 2 · answered Jan 24 '20 at 14:52

2

There is no magic. If you dig down into the method, eventually toString is called explicitly.

public static String valueOf(Object obj) {
    return (obj == null) ? "null" : obj.toString(); //in your case obj = the box in b1
}

answered Jan 24 '20 at 14:52

Michael

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How toString() overriding works

2 Answers2