Java的三种遍历方式

三种遍历方式：

普通for循环

增强for循环     

迭代器

import java.util.*;
//泛型擦除：泛型只在编译时存在，运行时消失
import java.util.Map.Entry;

public class BianLi {

    public static void main(String[] args) {
        run1();
        run2();
        run3();
    }
    //list集合
    public static void run1() {
        List<String> list = new ArrayList<String>();
        list.add("aaa");
        list.add("bbb");
        list.add("ccc");
        System.out.println("===================");
        
        //三种遍历集合方法：普通for循环     增强for循环      迭代器
        
        //普通for循环
        for(int i = 0;i < list.size();i++) {
            //有泛型限定，需转换成String类型
            String str = list.get(i);
            System.out.println(str);
        }
        
        System.out.println("==================");
        
        //增强for循环
        for(String str: list) {
            System.out.println(str);
        }
        
        System.out.println("==================");
        
        //迭代器
        Iterator<String> it1 = list.iterator();
        while(it1.hasNext()) {
            System.out.println(it1.next());
        }
            
        
    }
    //set集合
            public static void run2(){
                Set<String> set = new HashSet<String>();
                set.add("ddd");
                set.add("eee");
                set.add("fff");
                System.out.println("====================");
                //增强for循环
                for(String str: set) {
                    System.out.println(str);
                }
                
                System.out.println("====================");
                //迭代器
                Iterator<String> it2 = set.iterator();
                while(it2.hasNext()) {
                    System.out.println(it2.next());
                }
                
    }
            //map集合
            public static void run3() {
                System.out.println("====================");
                Map<String,String> map = new HashMap<String,String>();
                map.put("1","a");
                map.put("2","b");
                map.put("3","c");
                Set<String> keys = map.keySet();
                //迭代器
                Iterator <String> it = keys.iterator();
                while(it.hasNext()) {
                    String key = it.next();
                    String value = map.get(key);
                    System.out.println(key+":"+value);
                }
                //entry
                Set<Entry<String,String>> set = map.entrySet();
                for(Entry<String,String> entry : set) {
                    System.out.println(entry.getKey()+":"+entry.getValue());
                }
            }

}