实例变量的值在两个类中是不同的。为什么？ （+更多问题） [英] values of an instance variable is different in two classes. Why? (+ more questions)
问题描述
我有一个 TurnIndicator 类，它的方法 getTurn（）; 只是返回String的 BLACK，BLACK，然后在WHITE和BLACK之间交替。
I have a TurnIndicator class, and its method getTurn(); just returns String of "BLACK", "BLACK" and then alternates between "WHITE" and "BLACK".
在我的板类中，它结合了包中的所有类并使其一起工作，我创建了一个 TurnIndicator class， _turn ，并声明一个具有初始值 _t = _turn的实例变量 _t 。 getTurn（）;
然后，我为 _t定义了一个访问器方法 - getT（）。
Inside my Board class, which combines all classes in the package and make it work together, I created an instance of TurnIndicator class, _turn, and declared an instance variable _t with initial value _t = _turn.getTurn();
Then, I defined an accessor method for _t - getT().
现在，当我在板内打印类，它打印黑，黑等等。 _t
但是，当我在另一个类中使用 getT（）访问 _t 值时， SelectPieceListener ，这将打印 null 。
Now, when I print the _t value inside the Board class, it prints "BLACK", "BLACK", and so on.
However, when I access _t value using getT() in another class, SelectPieceListener, this prints null.
为什么是这样吗？
我附上下面的类定义。不相关的部分被删除。
I attach my class definitions below. Irrelevant parts are removed.
我最近要做的是取决于 c == _st.checkMoveImpossible（）条件是让游戏玩家选择两种选择 -
What I want to do eventually is depending on c == _st.checkMoveImpossible() condition, to make the game player choose between two options -
1。点击选择按钮（在这种情况下， _cmi 成为 1 和 selectClicked（）方法为 if（_cmi == 1） block。更具体地说，它改变了 _t 值的顺序，以便玩家跳过一圈）或
1. by clicking select button(in this case, _cmi becomes 1, and selectClicked() method do desired action for if(_cmi == 1) block. More specifically, it changes order of _t value, so that the player skips one turn), or
2。通过点击滚动按钮（在这种情况下， _cmi 成为 2 ，并在 scrollClicked（）方法中执行类似的操作，让当前玩家移动另一个玩家的作品。）
2. by clicking scroll button (in this case, _cmi becomes 2, and do similar thing in scrollClicked() method to let current player move the other player's piece.).
我只是把 _cmi == 1 案例动作工作，把所有内容放在 selectClicked（）方法，但是我必须提供 _cmi == 2 case（当玩家点击滚动按钮），所以我不得不将其与方法分离。
I made just the _cmi == 1 case action work, by putting everything inside selectClicked() method, but I had to provide _cmi==2 case(when the player clicked scroll button), so I had to decouple it from the method.
现在，我一直试图使它在 SelectPieceListener class，所以如果我成功，我可以稍后将它移动到 Board 类。
Now, I have been trying to make it work in SelectPieceListener class for now, so that I could move it to the Board class later if I succeed.
然而我做了几个小时的尝试都失败了。
我一次编码了一个或两个，这是我第一次使用很多类进行项目。我真的在这种事情上没有经验。
However, every attempt I made for hours failed. I have coded one class or two at a time, and this is my first time doing projects with many classes. I am really unexperienced at this kind of things.
如果你能给我一些建议，那将有助于我。
If you could give me some advice, that will help me a lot.
我知道这是非常繁琐的工作，但我可能无法自己做这个。
请花一些时间阅读代码并帮助我。
I know this is really tedious work, but I may not be able to do this by myself.. Please spend some time to read the code and help me.
public class Board {
private Structure _st;
private TurnIndicator _turn;
private String _t;
private int _cmi;
public Board() {
_turn = new TurnIndicator();
_t = _turn.getTurn();
_cmi = 0;
}
public ScrollListener getScroll(){
return _scroll;
}
public String getT() {
return _t;
}
public int setcmi(int cmi) {
return _cmi = cmi;
}
public void selectClicked(char dir) {
int index = _scroll.getX();
HNode<ArrayList<String>> current = _st.getPosition(index);
System.out.println("checkMoveImpossible() = " + _st.checkMoveImpossible());
System.out.println("_t in Board = " + _t);
if(!current.getDatum().isEmpty()) {
if(_t == current.getDatum().get(current.getDatum().size()-1) && _cmi == 0) {
if(0 <= index && index < 17 && index != _st.indexOfSpBack()) {
current.forward(_t, current.getDatum().size());
}
else if(17 <= index && index < 25) {
char direction = dir;
_st.start(current, direction);
}
else if(index == _st.indexOfSpBack()) {
current.backward(_t, current.getDatum().size()-1);
}
_t = _turn.getTurn();
System.out.println("turn is "+ _t);
display();
}
else if(_t != current.getDatum().get(current.getDatum().size()-1) && _cmi == 0) {
String s = _t == "WHITE" ? "BLACK" : "WHITE";
System.out.println("It's "+_t+"'s turn now and only "
+s+" can move this piece.");
}
}
if(_cmi == 1) {
_t = _turn.getTurn();
_cmi = 0;
System.out.println("_cmi if block is reached");
display();
}
update();
}
下面是SelectPieceListener类定义
below is the SelectPieceListener class definition
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class SelectPieceListener implements ActionListener {
private Board _board;
private Structure _st;
private String _t;
public SelectPieceListener(Board board) {
_board = board;
_st = _board.getStructure();
_t = _board.getT();
}
@Override
public void actionPerformed(ActionEvent e) {
char c = _t == "WHITE" ? 'b' : 'w';
_board.selectClicked('l');
System.out.println(_t);
if(c == _st.checkMoveImpossible()) {
String theOther = _t == "WHITE" ? "BLACK" : "WHITE";
System.out.println("No possible move for "+_t+": click select to skip turn, " +
"or click scroll to move " + theOther + " pieces.");
_board.setcmi(1);
_board.update();
_board.selectClicked('l');
}
}
}
推荐答案
嗯，
我看到你有一些我不推荐的东西。 SelectPieceListener中的_t和_st字段不是必需的，因为您可以从_board字段获取它们，为什么不需要重复引用？
I see you have some things I wouldn't recommend. The _t and _st fields in SelectPieceListener are not necessary as you can get them from the _board field, why keep duplicated references if it's not necessary?
另一方面，我看到你用==做很多String比较，你应该总是使用STRING_LITERAL.equals（variable）。
On the other hand, I see you do a lot of String comparisions with ==, you should always use "STRING_LITERAL".equals(variable).
之后，我建议您使用像Eclipse这样的IDE，以便您可以调试部分代码。如果您的变量为空，那么在某个时候可能会丢失，调试器将是找到问题的最佳方式。
After that, I would recommend you to use an IDE like Eclipse so you can debug parts of your code. If your variable is null, it's probably getting lost at some point, a debugger will be the best way to find the issue.
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