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为什么重写equals方法时必须重写hashcode方法
Java字符串不相同但HashCode相同的例子（算法）

Java字符串不相同但HashCode相同的例子

    public static void main(String[] args) {
        String a = "ABCDEa123abc";
        String b = "ABCDFB123abc";
        System.out.println(a.hashCode() == b.hashCode()); //输出true
    }

  public static void main(String[] args) throws InterruptedException {
        ConcurrentHashMap<String, String> map = new ConcurrentHashMap<String, String>();
        map.put("3Qj", "1");
        map.put("2pj", "2");
        map.put("2qK", "3");
        map.put("2r,", "4");
        map.put("3RK", "5");
        map.put("3S,", "6");
        map.put("42j", "7");
        map.put("43K", "8");
        map.put("44,", "9");


        Iterator<Map.Entry<String, String>> entryIterator = map.entrySet().iterator();
        while (entryIterator.hasNext()) {
            Map.Entry<String, String> v = entryIterator.next();
            System.out.println(v);

        }
    }

打印结果：

3Qj  ====  51628
2pj  ====  51628
2qK  ====  51628
2r,  ====  51628
3RK  ====  51628
3S,  ====  51628
42j  ====  51628
43K  ====  51628
44,  ====  51628

参考：字符串不相同出现相同HashCode（算法）