在java構造函數中實例化一個二維數組？

Question

我感到很困惑。 我需要創建一個構造函數來創建一個帶有從main方法調用的參數的二維數組。每次我在同一個類的另一個方法中調用Seats 2D數組時，我都會收到錯誤。 為什么這樣，我如何使用我在構造函數中創建的數組？

class MovieSeating 
{

public MovieSeating(int rowNum, int columnNum)
{
    String [][] Seats = new String[rowNum][columnNum];
    for (int r = 0; r < rowNum; r++)
    {
        for (int c = 0; c < columnNum; c++)
        {
            Seats[r][c] = "???";
        }
    }
}

private Customer getCustomerAt(int row, int col)
{
    System.out.println("Customer at row " + row + " and col " + col + "." );
    System.out.println(Seats[row][col]);

}

Answer 1

您處於良好的軌道上，但您必須制作Seats實例變量才能獲得正確的結果：

private String [][] Seats;
public MovieSeating(int rowNum, int columnNum)
{
    Seats = new String[rowNum][columnNum];
    for (int r = 0; r < rowNum; r++)
    {
        for (int c = 0; c < columnNum; c++)
        {
            Seats[r][c] = "???";
        }
    }
}

Answer 2

將構造函數外部的數組聲明為私有變量：

class MovieSeating 
{
    private String [][] Seats;
public MovieSeating(int rowNum, int columnNum)
{
    Seats = new String[rowNum][columnNum];
    for (int r = 0; r < rowNum; r++)
    {
        for (int c = 0; c < columnNum; c++)
        {
            Seats[r][c] = "???";
        }
    }
}

private void getCustomerAt(int row, int col)
{
    System.out.println("Customer at row " + row + " and col " + col + "." );
    System.out.println(Seats[row][col]);

}
}

Answer 3

class MovieSeating{

private String[][] seats;

public MovieSeating(int col, int row){
  seats = new String[row][col];
}
}

使座位成為實例變量以增加其范圍。

Answer 4

Seats在main是未知的，只有在構造函數的范圍內才知道。

你應該使它成為一個類成員並在構造函數中初始化它：

class MovieSeating  {
   private String [][] Seats;
   ..
   public MovieSeating(int rowNum, int columnNum) {
      Seats = new String[rowNum][columnNum];
      ..
   }
}

Answer 5

在這里我發送代碼剪切我希望這將有助於你

 public Charts(int graph_min, int graph_max, double[] dataset, int stepSize,double[][] percentRange) { //here double[][]={{10},{100}}; this(graph_min,graph_max,dataset); this.stepSize = stepSize; System.out.println("double constructor "+percentRange.length); this.percentRange = new double[percentRange.length][percentRange[0].length]; System.out.println("percentRange: "+this.percentRange); for (int i = 0; i < percentRange.length; i++) { for (int j = 0; j < percentRange[i].length; j++) { this.percentRange[i][j] = percentRange[i][j]; System.out.println("ps_Axis constructor valuesd "+this.percentRange[i][j]); } }