为什么列表中的所有元素看起来都一样？

Question

我有以下代码:

Integer[] lastExchange = new Integer[nColors];
Integer[] newExchange = new Integer[nColors];
while (true) {
    ...
    for (int i=0; i<nColors; i++) {
       lastExchange[i] = newExchange[i];
    }
    ...
    exchanges.add(lastExchange);
    output.log.fine("Exchange:" + lastExchange[0] + "," + lastExchange[1]);
}
for (Integer[] exchange : exchanges) {
    output.log.fine("Exchange:" + exchange[0] + "," + exchange[1]);
}

我有两个输出(一个在while循环中另一个在for循环中).第一个输出显示我确实在列表中添加了不同的数组.当我在第二个循环中进行双重检查时,我看到exchange列表中的所有元素都是相同的(它们等于列表的第一个元素).

有谁知道我在做错了什么？

Answer 1

正如展开的答案所述,您将在循环的每次迭代中添加对同一数组的引用.您需要每次创建一个新数组:

// It's not clear where newExchange is actually populated
Integer[] newExchange = new Integer[nColors];
while (true) {
    Integer[] lastExchange = new Integer[nColors];
    ...
    for (int i=0; i<nColors; i++) {
       lastExchange[i] = newExchange[i];
    }
    ...
    exchanges.add(lastExchange);
    output.log.fine("Exchange:" + lastExchange[0] + "," + lastExchange[1]);
}

或者,如果您只是克隆数组:

Integer[] newExchange = new Integer[nColors];
while (true) {
    Integer[] lastExchange = newExchange.clone();
    ...
    exchanges.add(lastExchange);
    output.log.fine("Exchange:" + lastExchange[0] + "," + lastExchange[1]);
}