如何重写String类的hashcode方法？

Question

I want to override String classes Hashcode / Equals methods as I know the String class is final and the method inside that can not be overridden. I have a scenario where I want to apply the same. for instance code is given below,

public static void main(String[] args) {

        Map<String,Integer> map = new HashMap();
        map.put("Mukul", 1);
        map.put("Aditya", 1);

        System.out.println(map);


    } 

As I am passing string as a key and map is gonna call String classes hashcode method implicitly. Now I want to declare that the given keys are same in my way. Please suggest if there is any way to do so?

Answer 1

You can create your own custom String class that contains a String member and implements equals and hashCode as you see fit, and use a Map<MyString,Integer> :

public class MyString {

    private String value;

    public MyString (String value) {this.value = value;}
    public int hashCode () {
        ...
    }
    public boolean equals (Object other) {
        ...
    }

    public static void main(String[] args) {

        Map<MyString,Integer> map = new HashMap<>();
        map.put(new MyString("Mukul"), 1);
        map.put(new MyString("Aditya"), 1);

        System.out.println(map);
    } 
}

Answer 2

As a comment already state to make a wrapper of the String class with its own hashcode and equals , here is another solution: you can use a TreeMap , and provide it with your own Comparator :

TreeMap<String, Integer> myMap = 
    new TreeMap<String, Integer>(new Comparator<Entry<String, Integer>>()
    {
        public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2)
        {
            return o1.getValue().compareTo(o2.getValue()); // your method here
        } 
    });

(inspired by Java TreeMap Comparator )

Answer 3

没有办法用字符串来做到这一点，而是创建自己的对象并在从地图中获取数据后对其进行处理。即使您创建自己的字符串类，也不会与已经存在的字符串类兼容，就像没有MyString obj = “名称”;