Java作业一

import java.util.ArrayList;
import java.util.Iterator;

public class Example04 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ArrayList list =new ArrayList();
		list.add("张三");
		list.add("李四");
		list.add("王五");
		Iterator it = list.iterator();
		while (it.hasNext()){
			Object obj = it.next();
			if("张三".equals(obj)){
				list.remove(obj);
			}
		}
		System.out.println(list);
	}
	
}

Java作业二

import java.util.TreeSet;
public class Example06{
    public static void main(String[] args){TreeSet ts=new TreeSet();
        ts.add(3);
        ts.add(29);
        ts.add(101);
        ts.add(21);
        System.out.println("创建的TreeSet集合为∶"+ts);
        System.out.println("TreeSet集合首元素为∶"+ts.first());
        System.out.println("TreeSet集合尾部元素为∶"+ts.last());
        System.out.println("集合中小于或等于9的最大的元素为∶"+ts.floor(9));
        System.out.println("集合中大于10的最小的元素为∶"+ts.higher(10));
        System.out.println("集合中大于100的最小的元素为∶"+ts.higher(100));
        Object first=ts.pollFirst();
        System.out.println("删除的第一个元素为："+first);
        System.out.println("删除第一个元素后TreeSrt集合变为："+ts);
    }
}

Java作业三

import java.util.HashSet;

class Student{
			private String id;
			private String name;
			
			public  Student (String id, String name){
				this.id =id;
				this.name = name;
			}
				public String toString(){
				return id +":"+name;
				}
				public int hashCode(){
					return id .hashCode();
				}
				public boolean equls (Object obj){
					if (this == obj){
						return true;
					}
					if(!(obj instanceof Student)){
						return false;
					}
					Student stu = (Student) obj;
					boolean b = this.id.equals(stu.id);
					return b ;
				}
			}
			

public class Example09 {
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		HashSet hs = new HashSet();
		Student stul = new Student("1","张三");
		Student stu2 = new Student("2","李四");
		Student stu3 = new Student("3","王五");
		hs.add(stul);
		hs.add(stu2);
		hs.add(stu3);
		System.out.println(hs);
	}

}