Iterator遍历List,Map和TreeMap的排序

package com.jiml.test;

import org.junit.Test;

import java.util.*;

public class TestIterator {

    @Test
    public void testIteratorList(){

        List<String> list = new ArrayList<>();
        list.add("aa");
        list.add("bb");
        list.add("cc");

        Iterator<String> iterator = list.iterator();
        while(iterator.hasNext()){
            String str = iterator.next();
            System.out.println(str);
        }


    }

    //使用keySet
    @Test
    public void testIteratorMap1(){

        Map<Integer,String> map = new HashMap<>();
        map.put(100,"aa");
        map.put(400,"bb");
        map.put(500,"cc");

        Iterator<Integer> iterator = map.keySet().iterator();
        while(iterator.hasNext()){
            Integer key = iterator.next();
            String value = map.get(key);
            System.out.println(key+"---"+value);
        }
    }

    //使用entrySet
    @Test
    public void testIteratorMap2(){

        Map<Integer,String> map = new HashMap<>();
        map.put(100,"aa");
        map.put(400,"bb");
        map.put(500,"cc");

        Iterator<Map.Entry<Integer, String>> iterator = map.entrySet().iterator();
        while(iterator.hasNext()){
            Map.Entry<Integer, String> entry = iterator.next();
            System.out.println(entry.getKey()+"---"+entry.getValue());
        }
    }

    //TreeMap按照key进行升降排序
    @Test
    public void testTreeMap1(){

        TreeMap<Integer,Integer> map1 = new TreeMap<>();
        TreeMap<Integer,Integer> map2 = new TreeMap<>(
                new Comparator<Integer>() {
                    @Override
                    public int compare(Integer o1, Integer o2) {
                        return o2-o1;
                    }
                }
        );



        map1.put(2,4);
        map1.put(1,2);
        map1.put(7, 1);
        map1.put(5,2);
        Iterator<Map.Entry<Integer, Integer>> iterator = map1.entrySet().iterator();
        while(iterator.hasNext()){
            Map.Entry<Integer, Integer> entry = iterator.next();
            System.out.println(entry.getKey()+"---"+entry.getValue());
        }
        System.out.println(map1);

        map2.put(2,4);
        map2.put(1,2);
        map2.put(7, 1);
        map2.put(5,2);
        Iterator<Map.Entry<Integer, Integer>> iterator1 = map2.entrySet().iterator();
        while(iterator1.hasNext()){
            Map.Entry<Integer, Integer> entry = iterator1.next();
            System.out.println(entry.getKey()+"---"+entry.getValue());
        }
        System.out.println(map2);


    }

    //TreeMap按照value值进行升降排序
    @Test
    public void testTreeMap2(){

        Map<String,String> map = new HashMap<>();
        map.put("a","9");
        map.put("b","8");
        map.put("c","7");
        map.put("d","1");
        System.out.println("map:"+map);

        Set<Map.Entry<String, String>> set = map.entrySet();
        List<Map.Entry<String, String>> list = new ArrayList<>(map.entrySet());

        Collections.sort(list, new Comparator<Map.Entry<String, String>>() {
            @Override
            public int compare(Map.Entry<String, String> o1, Map.Entry<String, String> o2) {
                return o1.getValue().compareTo(o2.getValue());
            }
        });

        System.out.println("list:"+list);

    }



}