public static void main(String[] args) {
        Map<String, String> map = new HashMap<String, String>();
        map.put("Tom", "CoreJava");
        map.put("John", "Oracle");
        map.put("Susan", "Oracle");
        map.put("Jerry", "JDBC");
        map.put("Jim", "Unix");
        map.put("Kevin", "JSP");
        map.put("Lucy", "JSP");
        // 增加一個新老師
        map.put("Allen", "JDBC");
        // Lucy教CoreJava
        map.put("Lucy", "CoreJava");
        // 遍歷Map，輸出所有的老師及老師教授的課程
        "/**
         * keySet()返回此映射關(guān)系中包含鍵的Set視圖
         */"
        Set<String> keys = map.keySet();
        for (String key : keys) {
            System.out.println(key + "教" + map.get(key));
        }

        '/**
         * 結(jié)果： 
         * Jerry教JDBC 
         * Jim教Unix 
         * Tom教CoreJava 
         * Susan教Oracle 
         * Lucy教CoreJava
         * John教Oracle
         *  Allen教JDBC 
         *  Kevin教JSP
         */'
        '/**
         * entrySet()方法：返回此映射中包含的映射關(guān)系的Set視圖
         */'
        System.out.println("***************************");
        Set<Map.Entry<String, String>> keysNew = map.entrySet();
        for (Map.Entry<String, String> key : keysNew) {
            // System.out.println(map.get(key)); //得到的是null
            System.out.println(key);
            /**
             * 結(jié)果： 
             * Jerry=JDBC 
             * Jim=Unix 
             * Tom=CoreJava
             * Susan=Oracle 
             * Lucy=CoreJava
             * John=Oracle 
             * Allen=JDBC 
             * Kevin=JSP
             * 
             */
        }

    }