Objects eligible for Garbage collector

Garbage collector

1. Isolation:
class A{
            A r;
            A(int i){
             //something   
           }
      } 

      A a1 = new A(100);
      a1.r = new A(101);
      a1.r.r = new A(102);
      a1.r.r.r = a1;

      a1  = null //all ojects are eligible to garbage collector
      
2.  A a = new A(100);
  a =new A(200); //new A(100) eligible for GC
  -------------------------------------------ex weak reference and weakhashmap-------------
  package com.gc.refrences;

import static com.jayway.awaitility.Awaitility.await;

import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.WeakHashMap;
import java.util.concurrent.TimeUnit;

class Employee {
	private String name;
	private int id;

	public Employee(String name, int id) {
		super();
		this.name = name;
		this.id = id;
	}

	
	public void setName(String name) {
		this.name = name;
	}


	public void setId(int id) {
		this.id = id;
	}


	public String getName() {
		return name;
	}

	public int getId() {
		return id;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + id;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Employee other = (Employee) obj;
		if (id != other.id)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}
}

public class WeakRefrencesDemo {
	public static void main(String[] args) {
		HashMap<Employee, String> hm = new HashMap<>();

		Employee e1 = new Employee("vikas", 1);
		Employee e2 = new Employee("Ram", 2);
		hm.put(e1, "vikas");
		hm.put(e2, "Ram");

		e1 = null;
		System.gc();
		
//		try {
//			await().atMost(10, TimeUnit.SECONDS).until(hm::isEmpty);
//		} catch (Exception e) {
//			// TODO Auto-generated catch block
//			e.printStackTrace();
//		}
		

		for (Employee key : hm.keySet()) {
			System.out.println(key.getName());
		}

		System.out.println("-----------");
		WeakHashMap<Employee, WeakReference<Employee>> whm = new WeakHashMap();

		Employee e11 = new Employee("vikas", 1);
		Employee e22 = new Employee("Ram", 2);
		
		 WeakReference<Employee> reference = new WeakReference(e11);
		whm.put(e11,reference);
		whm.put(e22, new WeakReference(e22));

		System.out.println(reference.get().getName() +":::");
		e22.setName("khk");// by changing this weak refrence will become null
		e11 = null;
		System.out.println(reference.get().getName() +":::::");
		//System.gc();
		
		System.out.println(reference.get().getName() +":::>::");
//		try {
//			await().atMost(10, TimeUnit.SECONDS).until(whm::isEmpty);
//		} catch (Exception e) {
//			// TODO Auto-generated catch block
//			e.printStackTrace();
//		}
		
		for (Employee key : whm.keySet()) {
			System.out.println(key.getName() +"**");
			System.out.println(whm.get(key).get().getName());
		}

	}
}