学习打卡4--集合类

该内容没有什么太难理解的地方，所以就只照书上的代码代码敲了一遍

ArrayList集合

package Collection;
import java.util.ArrayList;
import java.util.Iterator;
public class Collectiontest {

	public static void main(String[] args) {
		ArrayList<String> list = new ArrayList<String>();
		list.add("wahaha");
		list.add("kangshifu");
		list.add("ADgai");
		
		for(String str:list) {
			System.out.println(str);
		}
		//使用迭代器遍历集合
		Iterator<String> ite = list.iterator();
        while(ite.hasNext()) {  //判断是否有下一个元素
        	System.out.println(ite.next());
        }
        String[] s = new String[list.size()];
        list.toArray(s);
        for(int i=0;i<list.size();i++) {
        	System.out.println(s[i]);
        }
        }
	}

Set集合

package Collection;
import java.util.*;

public class UpdataStu implements Comparable<Object>{
	   String name;
	   long id;
	   
	   public UpdataStu(String name,long id) {
		   this.id = id;
		   this.name = name;
	   }
	 
	   public int compareTo(Object o){
		   UpdataStu upstu = (UpdataStu)o;
		   int result = id>upstu.id?1:(id==upstu.id ?0:-1);
		   return result;
	   }
	
	   public String getName() {
		   return name;
	   }
	
	   public void setName(String name) {
		   this.name = name;
	   }
	
	   public long getid() {
		   return id;
	   }
	    public void setid(long id) {
	    	this.id = id;
	    }
	   
       public static void main(String[] args) {
    	   UpdataStu stu1 = new UpdataStu("李同学",01011);
    	   UpdataStu stu2 = new UpdataStu("陈同学",01021);
    	   UpdataStu stu3 = new UpdataStu("王同学",01051);
    	   UpdataStu stu4 = new UpdataStu("马同学",01012);
    	   TreeSet<UpdataStu> tree = new TreeSet<UpdataStu>();
    	   HashSet<String> hash = new HashSet<String>();
    	   tree.add(stu1);
    	   tree.add(stu2);
    	   tree.add(stu3);
    	   tree.add(stu4);
    	   hash.add("first");
    	   hash.add("second");
    	   hash.add("first");
    	      System.out.println(hash);//集合中不能有重复元素，所以输出只有两个元素
    	   Iterator <UpdataStu> it = tree.iterator();
    	   while(it.hasNext()) {
    		   UpdataStu stu = (UpdataStu)it.next();//it.next()取出的是Object对象，所以这里需要强制转换
    		   System.out.println(stu.getid()+" "+stu.getName());
    	   }
    	   System.out.println("------------");
    	   it = tree.headSet(stu2).iterator();
    	   while(it.hasNext()) {
    		   UpdataStu stu = (UpdataStu)it.next();
    		   System.out.println(stu.getid()+"   "+stu.getName());
    	   }
       }
	

}

Map集合

package Collection;
import java.util.Map;
import java.util.HashMap;
import java.util.Iterator;
public class Test {
       public static void main(String[] args) {
    	   Map<String,String> map = new HashMap<String,String>();
    	   map.put("1", "lala");
    	   map.put("2","haha");
    	   map.put("3", "shadiao");
       for(String key:map.keySet()) {
    	   System.out.println(key+"   "+map.get(key));
       }
       
       //使用迭代器遍历map
       Iterator<Map.Entry<String,String>> it = map.entrySet().iterator();
       while(it.hasNext()) {
    	   Map.Entry<String,String>entry = it.next();
    	   System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
       }
    }
}