What will happen if none or only some fields are initialized in a constructor [duplicate]

Question

The purpose of a constructor is initializing values for the fields, setting the initial state of the object. So what will happen if some fields or all fields were not initialized in the constructor?

Is it calling a default constructor provided by the JVM before the user defined constructor?

So, in this example, what would be output?

class Name{
      int x;
      boolean y;


      Name(){
      // no initialize
     }

     public static void main(){
        Name n = new Name();
        System.out.println(n.x + ", " + n.y);
     }

 }

Answer 1

Class-level fields (instance or static fields) get default values assigned to them. This means that if the constructor or instance (or static) initialization blocks don't explicitly initialize these fields, the default values will remain.

In your case:

class Name{
      int x;     //default value for int is 0
      boolean y; //default value for boolean is false

In other words, your output should be 0, false

This question has details on the actual default values for primitive types. For Object data types, the default value is null (see also the data types documentation).