java - 为什么下面的代码只显示循环最后一圈的数组值？

Question

public static void displaySummary(int totalShipment,
                                  String[] nameOfBus,
                                  int[][] storageBox)
{
    int counter;

    //Display the Summary Report              
    System.out.println("\nSummary\n- - - - - - - - - - - -");
    for(counter = 0; counter < totalShipment; ++counter)
    {
        System.out.println("Shipment #" + (counter + 1)+  " - " + nameOfBus[counter]);
        System.out.print("\nXL - " + storageBox[0][counter] + ",");
        System.out.print("L - " + storageBox[1][counter] + ",");
        System.out.print("M - " + storageBox[2][counter] + ",");
        System.out.print("S - " + storageBox[3][counter]+"\n");
    }

    System.out.println("\nTotal Number of containers required for these shipments:\n");
    System.out.println("XL - " + totalXL);
    System.out.println("L - " + totalL);
    System.out.println("M - " + totalM);
    System.out.println("S - " + totalS);        
}

当我从 main 调用 displaySummary 时，无论发货数量是多少，都只会打印循环最后一圈的值...如果只有一次发货，则会打印这些值。如果两次发货，则打印第二圈循环的值，但第一圈不会打印......

Answer 1

这是一个典型的初学者错误。

如果您通过以下方式添加多个项目:

int n = 0;
int[] box = new int[4];

box[0] = ...; box[1] = ...; ...
storageBox[n] = box;
++n;

box[0] = ...; box[1] = ...; ...
storageBox[n] = box;
++n;

box[0] = ...; box[1] = ...; ...
storageBox[n] = box;
++n;

错误是，您刚刚创建的同一个对象 new int[] 被放置在 storageBox[0]、[1] 和 [2]。您多次覆盖 sama 数组 box[0..4] 直至最后一个值。

所以storageBox[0] == storageBox[2]并且它们的数组值是相同的。

对于每个 storageBox 项，您必须添加一个 new int[4]。