[exercise] HashSet

distinguish ：

import java.util.HashSet;

public class TestHashSet {
    public static void main(String[] args) {
        HashSet set=new HashSet();
        set.add(1);                     // In this case, the length is ：1   The content is ：1
        set.add(new Integer(1));        // In this case, the length is ：1         1
        set.add(new Integer("1"));      // In this case, the length is ：1         1
        set.add(new Integer('1'));      // In this case, the length is ：2        49
        set.add("1");                   // In this case, the length is ：3         1
        set.add('1');                   // In this case, the length is ：4         1
        set.add(new String("1"));       // In this case, the length is ：4         1    new String  It's redundant 
        System.out.println(set.size()); //4
        System.out.println(set);        //[1, 49, 1, 1]
    }
}