Java——集合篇

import java.util.*;
public class TestSet {
	public static void main(String[] args){
		Set set= new HashSet();//创建一个hashset集合

		//set添加元素
		Student s1 = new Student(1,"张三");
		Student s2 = new Student(2,"李四");
		Student s3 = new Student(3,"王五");
		Student s4 = new Student(4,"赵六");
		set.add(s1);
		set.add(s2);
		set.add(s3);
		set.add(s4);
		set.add("孙七");
		set.add(null);
		
		Iterator it = set.iterator();
		while(it.hasNext()){
			Object o = it.next();
			if(o instanceof Student){
				Student stu = (Student)o;
				System.out.println(stu.getSname());
			}else{
				System.out.println("该元素类型不能获取到名字");
			}
		}
	}
}

       for(Object o : set){
          if(o instanceof Student){
             Student stu = (Student)o;
             System.out.println(stu.toString());
          }
       }

List list = new ArrayList();
list.add(new Student());
list.remove(0);

Map map = new HashMap();//创建一个map集合

map.put("name","张三");  //value可以为字符串
map.put(new Integer(3),4);//可以为数值
map.put("stu1",new Student());//可以为对象
map.put("students",new ArrayList());//可以为集合

Map<String,String> map = new HashMap<>();
//第一种
for(Map.Entry<String,String> entry : map.entrySet()){
            String key = entry.getKey();
            String value = entry.getValue();
        }
//第二种   
for (String key : map.keySet()){
            String value = map.get(key);
}