Java自定义字符串哈希：通过包装类与hashCode()重写

import java.util.Objects;

public class MyString {
    private final String value; // 封装原始字符串

    public MyString(String value) {
        this.value = value;
    }

    public String getValue() {
        return value;
    }

    // 后续将在此处重写 equals() 和 hashCode()
}

    @Override
    public int hashCode() {
        // 自定义哈希实现：将所有字符的Unicode码点（ASCII值）求和
        // codePoints() 方法返回一个 IntStream，包含字符串中所有字符的码点
        return value.codePoints().sum();
    }

    @Override
    public boolean equals(Object o) {
        // 引用相等，直接返回true
        if (this == o) return true;
        // 如果是null或者类型不匹配，返回false
        if (o == null || getClass() != o.getClass()) return false;
        // 类型转换
        MyString myString = (MyString) o;
        // 比较封装的字符串值是否相等
        return Objects.equals(value, myString.value);
    }

import java.util.Objects;

public class MyString {
    private final String value;

    public MyString(String value) {
        this.value = value;
    }

    public String getValue() {
        return value;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        MyString myString = (MyString) o;
        return Objects.equals(value, myString.value);
    }

    @Override
    public int hashCode() {
        // 自定义哈希实现：将所有字符的Unicode码点（ASCII值）求和
        return value.codePoints().sum();
    }
}

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class CustomHashExample {
    public static void main(String[] args) {
        // 使用MyString作为HashMap的键
        Map<MyString, String> myMap = new HashMap<>();

        MyString s1 = new MyString("hello");
        MyString s2 = new MyString("world");
        MyString s3 = new MyString("olleh"); // 与"hello"字符相同，但顺序不同，hashCode可能相同

        myMap.put(s1, "Hello Value");
        myMap.put(s2, "World Value");
        myMap.put(s3, "Olleh Value");

        System.out.println("Map content:");
        for (Map.Entry<MyString, String> entry : myMap.entrySet()) {
            System.out.println("Key: " + entry.getKey().getValue() + ", HashCode: " + entry.getKey().hashCode() + ", Value: " + entry.getValue());
        }

        // 尝试获取
        MyString s1_lookup = new MyString("hello");
        System.out.println("\nRetrieving 'hello': " + myMap.get(s1_lookup)); // 应该能找到

        MyString s3_lookup = new MyString("olleh");
        System.out.println("Retrieving 'olleh': " + myMap.get(s3_lookup)); // 应该能找到

        // 注意：由于是字符ASCII值求和，"hello"和"olleh"的哈希码是相同的
        // 但是equals方法会判断字符串值是否相同，所以它们在HashMap中是不同的键
        System.out.println("\nHashCode for 'hello': " + s1.hashCode());
        System.out.println("HashCode for 'olleh': " + s3.hashCode());
        System.out.println("Are 'hello' and 'olleh' equal (MyString.equals)? " + s1.equals(s3));
        System.out.println("Are 'hello' and 'hello' equal (MyString.equals)? " + s1.equals(s1_lookup));

        // 使用MyString作为HashSet的元素
        Set<MyString> mySet = new HashSet<>();
        mySet.add(new MyString("apple"));
        mySet.add(new MyString("banana"));
        mySet.add(new MyString("apple")); // 再次添加"apple"，由于equals和hashCode，不会重复添加

        System.out.println("\nSet content:");
        for (MyString ms : mySet) {
            System.out.println("Element: " + ms.getValue() + ", HashCode: " + ms.hashCode());
        }
    }
}