推到堆栈Java后Word对象发生更改

我的类变量如下：

while(!paths.isEmpty()){
    BoggleSearchState2 path = paths.pop();

    if(dictionary.contains(path.getWord()) && !foundWords.contains(path.getWord())){
            foundWords.add(path.getWord());
    }

    int[][] grid = path.getGrid();
    int row = path.getRow();
    int column = path.getColumn();
    Letter[][] game = path.getGame();

    if(row < (grid.length-1) && grid[row+1][column] == 0) {
        paths.push(new BoggleSearchState2(path.getWordWord(), game[(row+1)][column], game));
    }
}

public BoggleSearchState2(Letter l, Letter[][] gameIn) {
    game = gameIn;
    word = new Word(l);
    grid = initialGrid(l);
    row = l.getPoint().y;
    column = l.getPoint().x;
    stringWord = wordToString(word);

}

public BoggleSearchState2(Word wordIn, Letter l, Letter[][] gameIn){
    game = gameIn;
    word = new Word(wordIn.getLetters());
    word.addLetter(l);
    grid = genGrid(word, game);
    row = l.getPoint().y;
    column = l.getPoint().x;
    stringWord = wordToString(word);

}

我遇到的问题是，在我按下新的BoggleSS2之后，我的path.word发生了变化，并添加了另一个字母对象。我不知道这是怎么发生的。谁能告诉我为什么

public class BoggleSearchState2 {

    private Word word;
    private Letter[][] game;
    private int[][] grid;
    private String stringWord;
    private int row, column;

公共类单词{
私有数组词；
公共词（字母l）{
word=新的ArrayList（）；
添加（l）；
}
公共单词（ArrayList listLetters，字母l）{
单词=列表字母；
添加（l）；
}
公共单词（ArrayList字母）{
单词=字母；
}

什么是

Word

类？Word类基本上只是一个字母对象的ArrayList。看起来您只是在复制周围的引用，所以内容的更改将反映在所有地方。您需要复制内容。请在构造函数中尝试

Word=new Word（new ArrayList（wordIn.getLetters（））；

。

public class Word {

private ArrayList<Letter> word;

public Word(Letter l) {
    word = new ArrayList<Letter>();
    word.add(l);
}
public Word(ArrayList<Letter> listLetters, Letter l){
    word = listLetters;
    word.add(l);
}
public Word(ArrayList<Letter> letters) {
    word = letters;
}