Public class Test{

    public static void main(String[] args){

        StringBuffer a = new StringBuffer("A");

        StringBuffer b = new StringBuffer("B");

        operator(a,b);

        System.out.println(a+","+b);

    }

    public static void operator(StringBuffer x,StringBuffer y){         x.append(y);y=x;     }

    public static void operator(StringBuffer x,StringBuffer y){

        x.append(y);y=x;

    }

}

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Java.util.HashMap map = new java.util.HashMap();

Map.put("name",null);

Map.put("name","Jack");

System.out.println(map.size());