How covariant method overriding is implemented using bridging Technique in java

Question

While reading on Covariant Overriding, i find out very strange fact,

covariant method overriding is implemented using a bridging technique. it also

Answer 1

Given the following two classes:

public class Node {
    private T data;
    public Node(T data) { this.data = data; }

    public void setData(T data) {
        System.out.println("Node.setData");
        this.data = data;
    }
}

public class MyNode extends Node {
    public MyNode(Integer data) {
 super(data); }
    public void setData(Integer data) {
        System.out.println("MyNode.setData");
        super.setData(data);
    }
}

When compiling a class or interface that extends a parameterized class or implements a parameterized interface, the compiler may need to create a synthetic method, called a bridge method, as part of the type erasure process.

To solve this problem and preserve the polymorphism of generic types after type erasure, a Java compiler generates a bridge method to ensure that subtyping works as expected. For the MyNode class, the compiler generates the following bridge method for setData:

class MyNode extends Node {

    // Bridge method generated by the compiler
    //
    public void setData(Object data) {
        setData((Integer) data);
    }

    public void setData(Integer data) {
        System.out.println("MyNode.setData");
        super.setData(data);
    }

    // ...
}