java集合之ArrayListHashMap遍历

Posted 2020-12-10 橘子酱ing

1、遍历ArrayList

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

public class ArrayListDemo1 {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        list.add("Hello ");
        list.add("World ");
        list.add("!!!");
        // foreach遍历
        for(String str:list){
            System.out.print(str);
        }
        System.out.println();
        // 将链表转为数组输出
        String [] str1 = new String[list.size()];
        list.toArray(str1);
        for (int i =0; i<str1.length;i++){
            System.out.print(str1[i]);
        }
        System.out.println();
        // 用迭代器遍历
        Iterator<String> iterator = list.listIterator();
        while (iterator.hasNext()){
            System.out.print(iterator.next());
        }
    }
}

2、遍历HashMap

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

public class MapIteratorDemo1 {
    public static void main(String[] args) throws Exception{
        Map<String,Integer> map = new HashMap<String, Integer>();
        map.put("壹",1);
        map.put("贰",2);
        map.put("叁",3);

        //通过Map.keySet遍历key和value
        for(String key:map.keySet()){
            System.out.println("key="+key+",value="+map.get(key));
        }
        System.out.println("****************");
        //通过Map.entrySet使用Iterator遍历key和value
        Iterator<Map.Entry<String,Integer>> iterator = map.entrySet().iterator();
        while (iterator.hasNext()){
            Map.Entry<String,Integer> entry = iterator.next();
            System.out.println("key="+entry.getKey()+",value="+entry.getValue());
        }
        System.out.println("****************");
        //容量大时，用
        for(Map.Entry<String,Integer> entry:map.entrySet()){
            System.out.println("key="+entry.getKey()+",value="+entry.getValue());
        }
        System.out.println("****************");

        for (int x :map.values()){
            System.out.println(x);
        }
    }
}