The output of an object passed to println method in Java programming

Question

I'm very much confused about the kind of Output I get when I pass different objects in println method. What I mean is; what the output of object in println method indicates? The following snippets may give a clearer idea about my Question.

    Integer i=10;
    Double d=23.45;
    String s="I'm";
    void display(){
        System.out.println(i);
        System.out.println(d);
        System.out.println(s);
        System.out.println(this);
    }

The code of My Main method:

    ObjectDemo o=new ObjectDemo();
    ObjectDemo o1=new ObjectDemo();
    ObjectDemo o2=new ObjectDemo();
    ObjectDemo o3=new ObjectDemo();
    ObjectDemo o4=new ObjectDemo();
    o.display();
    o1.display();
    o2.display();
    o3.display();
    o4.display();

ANd I get the following Output:

    I'm
    introductoryProgs.ObjectDemo@15db9742
    10
    23.45
    I'm
    introductoryProgs.ObjectDemo@6d06d69c
    10
    23.45
    I'm
    introductoryProgs.ObjectDemo@7852e922
    10
    23.45
    I'm
    introductoryProgs.ObjectDemo@4e25154f
    10
    23.45
    I'm
    introductoryProgs.ObjectDemo@70dea4e