为什么println打印引用对象的值而不是对象地址

Question

String myString="Plz_help";

I came to know that 'myString' is not an object but a object reference variable which stores the base address of the actual object. So 'myString' should return an address when i execute

System.out.println(myString);

but it is returning 'Plz_help' to the output.

Myclass obj_ref_var=new Myclass();

When I use the same System.out.println(obj_ref_var) for other class which I had created, it is returning the address.

Answer 1

When you call System.out.println on an object reference, system executes toString() method defined for the actual object that this reference refers to. For String this method returns its value.

Apparently, you haven't defined toString() method for your class that's why you get object classname + hashcode.

Answer 2

println knows about String s, and outputs their contents.

When you pass something other than a String into println , it implicitly calls that thing's toString method. The default toString on Object returns what you're seeing, which is not an address, but rather the name of the class, a @ , and the hex version of the object's hash code .

Answer 3

Well, System.out.println uses the reference to call the object's toString method.

As the toString() method of string returns the string itself, this is what printed.

But since you haven't override the toString method of MyClass , it returns the default toString , which is classname + hashcode.

Answer 4

When you System.out.println() an object, the println method checks if it's null and prints null if it is. If it isn't null, it calls the toString() method of the object. The toString() method of String overrides the Object.toString() method, to return itself.

Anyway, System.out.println() doesn't print the reference, it prints the object itself. The Object's implementation of toString() returns the class name of the object followed by its hashCode.