各种集合的遍历

Map遍历

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

public class MapTest {
    public static void main(String[] args) {
        Map<String, String> map = new HashMap<>();
        map.put("1", "1");
        map.put("2", "2");
        map.put("3", "3");
        map.put("4", "4");

        //通过Map.keySet遍历key和value
        for (String key : map.keySet())
            System.out.println(key + ":" + map.get(key));

        //通过Map.entrySet使用iterator遍历key和value
        Iterator<Map.Entry<String, String>> ito = map.entrySet().iterator();
        while (ito.hasNext()) {
            Map.Entry<String, String> entry = ito.next();
            System.out.println(entry.getKey() + ":" + entry.getValue());
        }

        //通过Map.entrySet遍历key和value
        for (Map.Entry<String, String> entry : map.entrySet())
            System.out.println(entry.getKey() + ":" + entry.getValue());

        //通过Map.values()遍历所有的value，但不能遍历key
        for (String value : map.values())
            System.out.println(value);
    }
}

List遍历

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

public class ListTest {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("1");
        list.add("2");
        list.add("3");
        list.add("4");

        //使用foreach遍历List
        for (String string : list)
            System.out.println(string);

        //变为数组相关的内容进行遍历
        String[] strArry = new String[list.size()];
        list.toArray(strArry);
        for (String str : strArry)
            System.out.println(str);

        //使用迭代器进行相关遍历
        Iterator<String> ito = list.iterator();
        while (ito.hasNext())
            System.out.println(ito.next());
    }
}