java - 2 个分离的对象由于某种原因连接在一起

Question

这是我的作业(作业)。我真的希望有人能帮助我弄清楚我做错了什么。

当我尝试创建一个 State 对象时状态 = 新状态(表大小，tb)；

然后尝试复制状态 st2 = new State(状态);

然后尝试修改state中的数据state.placeNumber(1,1,3);

由于某种原因，st2中的数据也发生了变化。

下面是代码。我真的希望有人能指出我的错误在哪里。

谢谢

public class State 
{

private int arraysize;
private int lastfilledx;
private int lastfilledy;
private int table[][];

//constructor

    public State()
    {

    }
    public State(State s)
    {
        arraysize = s.getsize();
        lastfilledx = s.lastindex_x();
        lastfilledy = s.lastindex_y();
        table = s.gettable();
    }
    public State(int size, int[][] tb)
    {
        arraysize = size;
        table = new int[size][size];        
        //copy the initial table which is a 2d array
        table = tb;     
        for (int i = 0 ; i < size; i++)
        {
            for(int j = 0 ; j < size ; j++)
            {
                 if ( table[i][j] == 1)
                 {

                    lastfilledx = i; 
                    lastfilledy =j;                   
                    break;
                 }
            }
        }
    }

public void placeNumber(int i, int j, int nextvalue)
{
    lastfilledx = i; 
    lastfilledy = j;    
    table[i][j] = nextvalue;
}   

public void printoutput()
{
        for (int i=0; i < arraysize; i++)
        {
            for (int j=0; j < arraysize; j++)
                System.out.print("  " + table[i][j]);

            System.out.println("");
        }

        System.out.println("last fill " + lastfilledx + " " + lastfilledy);
}

public int[][] gettable()
{
    return table;
}

public int getsize()
{
    return arraysize;
}
public int lastindex_x()
{
    return lastfilledx;
}
public int lastindex_y()
{
    return lastfilledy;
}
}




public class Dikuho extends State
{
    private static State state;

public static void main(String[] args) {

    int tablesize = 3;
    int tb[][] = new int[tablesize][tablesize];

    /*****HARDCODE the table data***/
    for (int i=0; i < tablesize; i++)
        for (int j=0; j < tablesize; j++)
            tb[i][j] = 0;


    //test case for 3x3
    tb[2][2] = 1;
    tb[0][0] = tablesize*tablesize;
    tb[0][1] = 7;
    tb[1][0] = 8;
    tb[2][1] = 2;       

    //initialize the state
    state = new State(tablesize, tb);


    **//Here is where the problem is. I only change the data in state but the data in st2 is also changed. I'm not sure what happen here.**
    State st2 = new State(state);   
    state.placeNumber(1,1,3);

    st2.printoutput();    **//These both printout same output which is not correct**    
    state.printoutput();
    }


}

Answer 1

您的复制构造函数已对 table 二维数组进行了浅复制。原始对象和副本都引用相同的原始数组，因为您将原始对象的数组引用分配给新对象。这对于 int 值来说很好，因为这些值是被复制的。但这对于对象来说不行，因为对象的引用被复制。

而不是仅仅复制对数组的引用...

table = s.gettable();

您需要创建一个新的复制数组:

table = new int[arraysize][arraysize];
// 2 nested for loops here to copy the contents