java Map接口的使用

小鱼儿 2022-05-27 02:45 263阅读 0赞

新建一个学生类，包含的成员变量有学号、姓名以及年龄，然后建立一个测试类，以学号作为键，学生类的对象作为值，保存到Map中，并实现输出，这里主要讲输出访时，核心就是迭代器。

package helloworld;
    
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Comparator;
    import java.util.Iterator;
    import java.util.List;
    
    public class StudentTest {
    
    	public static void main(String[] args) {
    		List<Student> stu = new ArrayList<Student>();
    		Student stu1 = new Student("1000", "aaa", 18);
    		Student stu2 = new Student("1001", "bbb", 19);
    		Student stu3 = new Student("1002", "ccc", 18);
    		Student stu4 = new Student("1001", "ddd", 20);
    		
    		stu.add(stu1);
    		stu.add(stu2);
    		stu.add(stu3);
    		stu.add(stu4);
    		
    		Iterator<Student> it = stu.iterator();
    		while(it.hasNext()){
    			System.out.println(it.next());
    		}
    		Collections.sort(stu, new Comparator<Student>(){
    
    			@Override
    			public int compare(Student o1, Student o2) {
    				if(o1.id.compareTo(o2.id) == 0){
    					return o1.age-o2.age;
    				}
    				return o1.id.compareTo(o2.id);
    			}	
    		});
    		System.out.println("-----------");	
    		Iterator<Student> it1 = stu.iterator();
    		while(it1.hasNext()){
    			System.out.println(it1.next());
    		}
    		
    	}
    }

package helloworld;
    
    import java.util.*;
    import java.util.Map.Entry;
    
    public class StudentTest3 {
    
    	public static void main(String[] args) {
    		Map<String, Student> map = new HashMap<String, Student>();
    		
    		Student stu1 = new Student("1000", "aaa", 18);
    		Student stu2 = new Student("1001", "bbb", 19);
    		Student stu3 = new Student("1002", "ccc", 18);
    		Student stu4 = new Student("1003", "ddd", 20);
    		
    		map.put(stu1.id, stu1);
    		map.put(stu2.id, stu2);
    		map.put(stu3.id, stu3);
    		map.put(stu4.id, stu4);
    		
    		
    		//1\利用键值对
    		Set<String> keyset = map.keySet();
    		Iterator<String> it = keyset.iterator();
    		while(it.hasNext()){
    			String nextkey = it.next();
    			Student obj = map.get(nextkey);
    			System.out.println(nextkey +"--"+obj);
    		}
    		System.out.println("************");
    		//2利用键值对德集合
    		Set<Entry<String, Student>> entrySet = map.entrySet();
    		Iterator<Entry<String, Student>> it1 = entrySet.iterator();
    		while(it1.hasNext()){
    			Entry<String, Student> entry = it1.next();
    			String id = entry.getKey();
    			Student stu = entry.getValue();
    			System.out.println(id+"---"+stu);
    		}
    		System.out.println("************");
    		//3
    		Collection<Student> col = map.values();
    		Iterator<Student> it2 = col.iterator();
    		while(it2.hasNext()){
    			Student stu0 = it2.next();
    			System.out.println("----"+stu0);
    		}
    	}
    
    }

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