Initialization of Instance Variables in Java

Initialization of Instance Variables in Java

How does instance variable id gets initialized to 0 when we have provided
our own default constructor and did not initialize id in it? The output
comes to be id:0 status:B How is id 0?
`class Demo{
private int id;
private char status;
public Demo(){
status = 'B';
}
public void display(){
System.out.println("Id:="+id+" Status:"+status);
}
public static void main(String args[]){
Demo ob = new Demo();
ob.display();
}
}`