Hashtable返回null但存在对象键(Hashtable returning null but object key is present)

 编辑：FML！ 我对哈希码的实现有一个小写的c。 -.- 
 
 我一直在努力学习TDD并一直关注Kent Beck的“By Example”一书; 这很好！ 
 
 但是，我似乎无法进步，因为当我访问哈希表时，值返回null。 我运行了一个调试会话，带有值的对象显然是结果为null。 
 
 构建和访问的代码是： 
 
public void addRate(String from, String to, int rate){
    this.rates.put(new Pair(from, to), new Integer(rate));
}
 
 来自和来自“GBP”和“USD”。 也通过调试验证。 
 
 调用上面的测试用例： 
 
@Test
public void testreduceMoneyDifferentCurrency(){
    Bank bank = new Bank();
    bank.addRate("GBP", "USD", 2);
    Money result = bank.reduce(Money.gbpound(2), "USD");
    assertEquals(Money.dollar(1), result);
}
 
 银行中的reduce方法调用方法速率： 
 
public Money reduce(Bank bank, String to){
    int rate = bank.rate(this.currency, to);
    return new Money(this.amount / rate, to);
}
 
 问题出在哪里： 
 
    public int rate(String from, String to){
    if (from.equals(to)) return 1;
    Integer rate = (Integer) this.rates.get(new Pair(from, to));
    return rate.intValue();
}
 
 第一行应对美元 - >美元转换等。 
 
 Pair对象是2个用作键的字符串。 
 
 我没有使用过很多表但是我看不出问题是什么，我确定这些值在哈希表中但是'rate'总是返回一个空值。 
 
 我无法看到树木。 :)有人能指出我正确的方向吗？ 

EDIT: FML! MY implementation of hashcode had a lowercase c. -.-
 
I've been trying to learn TDD and have been following the 'By Example' book by Kent Beck; it's very good!
 
However, I can't seem progress because a value is returning null when I access a hashtable. I've run a debug session and the object with the value is clearly there yet the result is null.
 
The code to build and access is:
 
public void addRate(String from, String to, int rate){
    this.rates.put(new Pair(from, to), new Integer(rate));
}
 
from and to are "GBP" and "USD". Also verified by debug.
 
Test case calling the above: 
 
@Test
public void testreduceMoneyDifferentCurrency(){
    Bank bank = new Bank();
    bank.addRate("GBP", "USD", 2);
    Money result = bank.reduce(Money.gbpound(2), "USD");
    assertEquals(Money.dollar(1), result);
}
 
The reduce method in bank calls the method rate:
 
public Money reduce(Bank bank, String to){
    int rate = bank.rate(this.currency, to);
    return new Money(this.amount / rate, to);
}
 
Which is where the issue is:
 
    public int rate(String from, String to){
    if (from.equals(to)) return 1;
    Integer rate = (Integer) this.rates.get(new Pair(from, to));
    return rate.intValue();
}
 
The first line copes with USD -> USD conversions etc. 
 
The Pair object is 2 strings built to be used as a key. 
 
I've not used has tables a great deal but I can't see what the issue is, I know for certain that the values are in the hashtable but 'rate' is always returning a null value.
 
I can't see the wood for the trees. :) Could someone point me in the right direction please?

原文：https://stackoverflow.com/questions/29922190