Why different behavious when referencing to an ArrayList Object than to an Integer Object in Java?

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In the code below if an ArrayList points to another ArrayList and if I changed the latter then the first ArrayList will change too, but the story is different for Obejct of type Integer!

Integer a= new Integer(10)
Integer b = a;
a = 20; // but b still remains 10

Why in the code below aList changes but not i?

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
    public class MyClass {
    Integer i = null;
    List<Integer> aList=new ArrayList<>();

    public MyClass(Integer data){
        this.i = data;
    };
    public MyClass(List<Integer> alist){
        this.aList = alist;
    };
    public static void main(String[] args) {
        List<Integer> intList = new ArrayList<>(Arrays.asList(1,2,3));
        MyClass c1 = new MyClass(intList);

        // after this line the c1.aList points to intList
        // so if I change intList, the c1.aList will change too
        System.out.println(Arrays.toString(c1.aList.toArray())); //[1, 2, 3]
        intList.remove(0);
        System.out.println(Arrays.toString(c1.aList.toArray()));
        //[2, 3] (1 is removed from  c1.aList too

        // but different story for object of type Integer
        Integer k = new Integer(10);
        MyClass c2 = new MyClass(k);
        k = 20;
        System.out.println(c2.i);
        // why still prints 10! not 20? after all c2.i used to point to k! 
    }
}

asked 28 secs ago

C graphics

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Why different behavious when referencing to an ArrayList Object than to an Integer Object in Java?