为什么这个String.equals（）方法总是返回false？ [英] Why does this String.equals() method always return false?

问题描述

我有我实现了自定义哈希code（）和equals（Object）方法使用Eclipse方法生成的类。类的每个对象都有一个称为String域 MUID 这应该是唯一的，足以确定相等。在覆盖的方法是这样的：

I have a class for which I have implemented a custom hashCode() and equals(Object) method using the Eclipse method generator. Each object of the class has a String field called mUid which should be unique and is enough to determine equality. The overridden methods look like this:

    @Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((mUid == null) ? 0 : mUid.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;
    DataSource other = (DataSource) obj;
    if (mUid == null) {
        if (other.mUid != null)
            return false;
    } else if (!mUid.equals(other.mUid))
        return false;
    return true;
}

但由于某些原因，当我比较我的类的两个对象，它始终返回false。我已经通过了code加强与调试，并可以确定MUID字符串相同。但我的等于（对象）方法始终返回该行

如果{返回false;}（mUid.equals（other.mUid）！）。

这意味着字符串equals（）方法是说字符串不相等。但是，在调试我可以看到，即使他们的哈希codeS都是平等的。

This means the String equals() method is saying the strings are not equal. But, in the debugger I can see that even their hashcodes are equal.

下面是一个调试截图：

任何人都可以请解释发生了什么事？
谢谢你。

Here is a debugging screenshot: Can anyone please explain what is happening? Thanks.

我要指出，我不打电话了equals（...）方法直接，而是来自列表＆LT;＆数据源GT; list.contains（数据源）。事实证明，如果我通过步等于（对象） code，它表明我，它在列表（每个对象比较，即使有返回false匹配）。但似乎在 List.contains（）方法返回正确的值（true或false）反正。不知道这是为什么，但它的作品。我曾在如果（list.contains（数据源））一个额外的分号; 所以我无法正确地看到包含（）是工作的罚款。 感谢您​​的帮助大家

I should point out that I am not calling the equals(...) method directly, but rather from List<DataSource> list.contains(DataSource). It turns out that if I step through the equals(Object) code, it shows me that it returns false for comparing every object in the list (even if there is a match). But it seems the List.contains() method returns the right value (true or false) anyway. Don't know why this is, but it works. I had an extra semicolon after the if(list.contains(dataSource)); so I could not rightly see that contains() was working fine. Thanks for your help everyone.

推荐答案

您的方法应该工作。我只是这个code测试，它工作得很好：

Your method should work. I just tested with this code and it worked fine:

public class DataSource {

    private String mUid;

    public DataSource(String m) {
        mUid = m;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((mUid == null) ? 0 : mUid.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;
        DataSource other = (DataSource) obj;
        if (mUid == null) {
            if (other.mUid != null)
                return false;
        } else if (!mUid.equals(other.mUid))
            return false;
        return true;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        DataSource ds1 = new DataSource("test");
        DataSource ds2 = new DataSource("test");
        System.out.println(ds1.equals(ds2));
    }

}

控制台输出是真;
当我改变了code到数据源DS2 =新的DataSource（测试1）; 它返回假;

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