在HashSet中更改值

Question

我已经读过这个问题:更改集合中的元素会改变'equals'语义

但是,我不知道如何解决我无法更改HashSet中的项目并在以后删除它的问题.

我有一些示例源代码:

public static void main(String[] args) {
    TestClass testElement = new TestClass("1");
    Set<TestClass> set = new HashSet<>();
    set.add(testElement);
    printIt(testElement, set, "First Set");
    testElement.setS1("asdf");
    printIt(testElement, set, "Set after changing value");
    set.remove(testElement);
    printIt(testElement, set, "Set after trying to remove value");
    testElement.setS1("1");
    printIt(testElement, set, "Set after changing value back");
    set.remove(testElement);
    printIt(testElement, set, "Set removing value");
}

private static void printIt(TestClass hullo, Set<TestClass> set, String message) {
    System.out.println(message + " (hashCode is " + hullo.hashCode() + "):");
    for (TestClass testClass : set) {
        System.out.println("    " + testClass.toString());
        System.out.println("        HashCode: " + testClass.hashCode());
        System.out.println("        Element is equal: " + hullo.equals(testClass));
    }
}

其中TestClass只是一个包含变量(加上getter和setter)并且实现了hashcode()和equals()的POJO.

有一个请求显示equals()和hashcode() - 方法.这些是由eclipse自动生成的:

@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((s1 == null) ? 0 : s1.hashCode());
    return result;
}

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    TestClass other = (TestClass) obj;
    if (s1 == null) {
        if (other.s1 != null)
            return false;
    } else if (!s1.equals(other.s1))
        return false;
    return true;
}

结果如下:

First Set (hashCode is 80):
    TestClass [s1=1]
        HashCode: 80
        Element is equal: true
Set after changing value (hashCode is 3003475):
    TestClass [s1=asdf]
        HashCode: 3003475
        Element is equal: true
Set after trying to remove value (hashCode is 3003475):
    TestClass [s1=asdf]
        HashCode: 3003475
        Element is equal: true
Set after changing value back (hashCode is 80):
    TestClass [s1=1]
        HashCode: 80
        Element is equal: true
Set removing value (hashCode is 80):

当哈希码发生变化时,我无法从HashSet中删除该值.在链接的问题中,我理解为什么会这样,但我不知道如何删除更改的值.有没有可能这样做？

Answer 1

您遇到了问题,因为哈希集中的键不是不可变的.如果您没有不可变密钥,则修改后将丢失原始密钥对象的引用.并且永远无法处理它,有时也称为集合中的内存泄漏.因此,如果您使用不可变密钥,则不会遇到这种情况.