Java中的不同遍历方式

已知一个Person类：

public class Person implements Comparable<Person>{
    String name;
    String id;
    public Person(String name,String id) {
        this.name=name;
        this.id=id;
    }
    
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public boolean equals(Object o) {
        if(!(o instanceof Person)) {
            return false;
        }
        Person person=(Person) o;
        return this.id.equals(person.id);
    }
    @Override
    public int compareTo(Person o) {
        if(o==null)
            return 1;
        return this.id.compareTo(o.id);
    }    

    public String toString() {
        return String.format("%s-%s", name,id);
    }
    
    public int hasCode() {
        return id.hashCode();
    }
}

1、遍历HashMap的不同方法：

import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import difficult.Person;
public class HashMapDemo {
    public static void main(String[] args) {
        Map<String, Person> map=new HashMap<>();
        Person p1=new Person("张三", "123");
        map.put(p1.getId(), p1);
        map.put("1002", new Person("1002", "李四"));
        map.put("1003", new Person("1003", "王五"));
        System.out.println(map);
        
        System.out.printf("%s-%s\n","1002",map.get("1002"));
        //增强型for，元素类型为Entry<String,Person>
        for(Entry<String, Person> entry:map.entrySet()) {
            System.out.printf("%s-%s ",entry.getKey(),entry.getValue());
        }
        System.out.println();
        //利用set来遍历
        Set<String> keys=map.keySet();
        for(String key:keys) {
            Person value=map.get(key);
            System.out.printf("%s-%s ",key,value);
        }
        System.out.println();
    }
}

2、遍历list的不同方法

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

import difficult.Person;

public class IterateList {

    public static void main(String[] args) {
        List<Person> persons = new ArrayList<>();//，List为一个接口，定义一个泛型为Person的ArrayList表
        Person p = new Person("1001", "张三");
        
        persons.add(p);
        persons.add(p);
        persons.add(new Person("1002", "李四"));
        persons.add(new Person("1003", "王五"));
        persons.add(new Person("1004", "沈六"));
        
        //遍历1：下标
        int len=persons.size();
        for(int i=0;i<len;i++) {
            Person person=persons.get(i);
            System.out.print(person+"\t");
        }
        System.out.println();
        //遍历2：迭代器
        Iterator<Person> iterator=persons.iterator();
        while(iterator.hasNext()) {
            Person person=iterator.next();
            System.out.print(person+"\t");
        }
        System.out.println();
        
        //遍历3：增强型for
        for(Person person:persons) {
            System.out.print(person+"\t");
        }
        System.out.println();
        
        int[] data= {1,3,5,7,9};
        for(int dat:data) {
            System.out.print(dat+"\t");
        }
    }
}

3、利用向量（通过枚举）遍历list

import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.Vector;

import difficult.Person;

public class VectorAndList {

    public static void main(String[] args) {
        List<Person> persons = new ArrayList<>();
        Person p = new Person("1001", "张三");
        
        persons.add(p);
        persons.add(p);
        persons.add(new Person("1002", "李四"));
        persons.add(new Person("1003", "王五"));
        persons.add(new Person("1004", "沈六"));
        
        // 遍历二：迭代器
        Iterator<Person> iterator=persons.iterator();
        while(iterator.hasNext()) {
            Person person=iterator.next();
            System.out.print(person+"\t");
        }
        System.out.println();
        
        //向量
        Vector<Person> vector=new Vector<>();
        vector.addAll(persons);
        //通过枚举遍历
        Enumeration<Person> enu=vector.elements();
        while(enu.hasMoreElements()) {
            Person person=enu.nextElement();
            System.out.print(person+"\t");
        }
        System.out.println();
        
    }
}