2021/10/31

某班共44名同学，每名同学都有姓名，学号和年龄等属性，使用JAVA内置迭代器实现对同学信息的遍历，要求按照学号从小到大和从大到小两种次序输出学生信息。

代码：

Iterator.java

package test;

interface Iterator {
	public Object next();
	public boolean hasNext();
	public boolean isFirst();
	public Object previous();
	public void setCursor(int i);
}

ConcreteAggregate.java

package test;

import java.util.ArrayList;
import java.util.List;

class ConcreteAggregate implements Aggregate {
	private List list = new ArrayList();
	public void add(Object obj) {
		list.add(obj);
	}
 
	public Iterator iterator() {
		return new ConcreteIterator(list);
	}
 
	public void remove(Object obj) {
		list.remove(obj);
	}
}

ConcreteIterator.java

package test;

import java.util.ArrayList;
import java.util.List;

public class ConcreteIterator implements Iterator{
	private List list = new ArrayList();
	private int cursor =0;
	public ConcreteIterator(List list){
		this.list = list;
	}
	public boolean hasNext() {
		if(cursor==list.size()){
			return false;
		}
		return true;
	}
	
	public boolean isFirst() {
		if(cursor==0) {
			return false;
		}
		return true;
	}
	
	
	public Object next() {
		Object obj = null;
		if(this.hasNext()){
			obj = this.list.get(cursor++);
		}
		return obj;
	}
	
	public void setCursor(int i) {
		cursor=i;
	}
	
	public Object previous() {
		Object obj=null;
		if(this.isFirst()) {
			obj=this.list.get(--cursor);
		}
		return obj;
	}
}

Aggregate.java

package test;

interface Aggregate {
	public void add(Object obj);
	public void remove(Object obj);
	public Iterator iterator();

}

Client.java

package test;

public class Client {
	public static void main(String[] args){
		Aggregate ag = new ConcreteAggregate();
		System.out.println("信1305班学生:");
		for(int i=1;i<=44;i++) {
			int m=20130000+i;
			String s=Integer.toString(m);
			ag.add(s+"    同学"+i);
			m=0;
			s=null;
		}
		Iterator it = ag.iterator();
		System.out.println("***************************");
		System.out.println("*      按学号从小到大输出       *");
		System.out.println("***************************");
		while(it.hasNext()){
			String str = (String)it.next();
			System.out.println(str);
		}
		System.out.println("***************************");
		System.out.println("*      按学号从大到小输出       *");
		System.out.println("***************************");
		it.setCursor(44);
		while(it.isFirst()){
			String str = (String)it.previous();
			System.out.println(str);
		}
	}
}