java中的list map set

public class dome {
public void setDemo() {
Set set = new HashSet();//这个是无序的
Set set = new TreeSet();//这个是有序的
String s1=new String("hello");
String s2 = s1+s1;
String s3 = new String("world");
//添加
set.add(s1);
set.add(s2);
set.add(s3);
System.out.println(set.size());

    boolean isExists =false;
    Iterator iterator=set.iterator();
    while (iterator.hasNext()) {
        String oldStr=(String) iterator.next();
        System.out.println(oldStr);
        
        
        /*
        if(s3.equals(oldStr)) {
            isExists=true;
            System.out.println("SDD");
        }*/
    }
}

public void listDemo() {
    List list =new ArrayList();
    list.add("ddd");
    list.add("sss");
    
    for(int i=0;i<list.size();i++) {
        System.out.println(list.get(i));
    }
    Iterator it =list.iterator();
    while(it.hasNext()) {
        boolean bl=false ;
        list.contains("sss");
        System.out.println(it.next());
    }
}
public void mapDemo() {
    Map map = new  HashMap();
    map.put("a", "1");
    map.put("b", "2");
    map.put("c", "3");
    map.put("d", "4");
    System.out.println(map.get("a"));
    System.out.println(map.get("b"));
    System.out.println(map.get("c"));
    System.out.println(map.get("d"));
    
}
public static void main(String[] args) {
    dome s=new dome();
    s.mapDemo();
}

}