Map集合的常用方法-蒲公英云

Map集合的常用方法

Object put(Object key, Object value)返回值是被替换的值。
    Object remove(Object key)    //删除该Map中key所对应的键值对
    void putAll(Map mapping)    //在Map后面追加新的键值对，如果Map中已包含新Map中的key则将key所对应的value用新value覆盖
    void clear()        //清空Map中的键值对，使其为空
    Object get(Object key)    //根据key获取对应value
    boolean containsKey(Object key)    //判断该Map中是否包含指定key，包含则返回true,否则返回false
    boolean containsValue(Object value)    //判断Map中是否包含指定value,包含则返回true,否则返回false
    int size()    //返回该Map的大小
    boolean isEmpty()    //判断该Map是否为空，如果为空则返回true,否则返回false。
    public Set keySet()    
    public Collection values()
    public Set entrySet()
    public class MapTest {
    public static void main(String[] args) {
            //put();
            //remove();
            //putAll();
            //clear();
            //get();
            //containsKey();
            //containsValue();
            //size();
            //isEmpty();
            // keySet();
            //values();
            //entrySet();
    }
    //返回键值对
    public static void entrySet() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        Set<Map.Entry<String,String>> strSet = strMap.entrySet();
        for (Entry<String, String> entry : strSet) {
            System.out.println(entry);
        }
    }
    //返回值的集合
    public static void values() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        Collection<String> values=strMap.values();
        for (String value : values) {
            System.out.println(value);
        }
    }
    //返回键的集合
    public static void keySet() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        Set<String> strSet=strMap.keySet();
        for (String str : strSet) {
            System.out.print(str+"\t");
        }
    }
    //判断该Map是否为空，如果为空则返回true,否则返回false。
    public static void isEmpty() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        Map<String,String> strMap01 = new HashMap<String,String>();
        boolean flag = strMap.isEmpty();
        boolean flag01=strMap01.isEmpty();
        System.out.println(flag+"\t"+flag01);
    }
    //返回该Map的大小
    public static void size() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        int mapSize = strMap.size();
        System.out.println("该Map大小为:"+mapSize);
    }
    //判断该Map中是否包含所指定value,若包含则返回true,否则返回false
    public static void containsValue() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        boolean flag = strMap.containsValue("aaa");
        boolean flag01=strMap.containsValue("qqq");
        System.out.println(flag+"\t"+flag01);
    } 
    //判断该Map中是否包含指定key,如果包含则返回true,否则返回false。
    public static void containsKey() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        boolean flag = strMap.containsKey("a");
        boolean flag01=strMap.containsKey("q");
        System.out.println(flag+"\t"+flag01);
    }
    //获取key所对应的value
    public static void get() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        String value=strMap.get("a");
        System.out.println(value);
    }
    //清空Map中的键值对，使其为空
    public static void clear() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        for (Map.Entry<String, String> keyValue : strMap.entrySet()) {
            System.out.println(keyValue);
        }
        strMap.clear();
        System.out.println("执行该方法后:");
        for (Map.Entry<String, String> keyValue : strMap.entrySet()) {
            System.out.println(keyValue);
        }
    }
    //将指定Map追加到Map中，如果所包含key已存在，则所对应的value将被覆盖
    public static void putAll() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        Map<String,String> strMap01 = new HashMap<String,String>();
        strMap.put("a", "abc");
        strMap.put("c", "asx");
        strMap.put("h", "hhh");
        for (Map.Entry<String, String> keyValue : strMap.entrySet()) {
            System.out.println(keyValue);
        }
        strMap.putAll(strMap01);
        for (Map.Entry<String, String> keyValue : strMap.entrySet()) {
            System.out.println(keyValue);
        }
    }
    //根据键从Map中删除对应键值对
    public static void remove() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        for (Map.Entry<String, String> keyValue : strMap.entrySet()) {
            System.out.println(keyValue);
        }
        strMap.remove("a");
        for (Map.Entry<String, String> keyValue : strMap.entrySet()) {
            System.out.println(keyValue);
        }
    }
    //新增一个键值对，如果该键已存在，则新的值会覆盖旧的值。
    public static void put() {
        Map<String,String> strMap = new HashMap<String,String>();
        strMap.put("a", "aaa");
        strMap.put("b", "bbb");
        strMap.put("c", "ccc");
        strMap.put("d", "ddd");
        strMap.put("e", "eee");
        strMap.put("f", "fff");
        for (Map.Entry<String, String> keyValue : strMap.entrySet()) {
            System.out.println(keyValue);
        }
        strMap.put("a", "abc");
        for(Map.Entry<String, String> keyValue : strMap.entrySet()) {
            System.out.println(keyValue);
        }
    }
}