Question

我在Java程序中遇到问题，当我尝试创建一个对象数组时。线程“main”中的异常java.lang.NullPointerException错误是我得到的错误。我真的可以使用一些帮助，因为我在这个地方被困了几个小时......

感谢您的帮助！

public class Placement extends JFrame  {
    private JPanel placementPanel;

    private JFrame gameEngineFrame;




    private Ship[] boardShips; //Array of ships objects to save ships
    private JButton[] shipButton; //Array of buttons for the ships
    private JLabel selectShipLabel;
    private Ship shipSelected;
    private Ship highlightedShip;





        JPanel shipSelect = new JPanel();
        shipSelect.setLayout(new GridLayout(14, 1));
        shipSelect.setBackground(Color.getHSBColor(0.0F, 0.0F, 0.75F)); //Setting background color. Hue, saturation, brightness format. (HSB)
        shipSelect.setBounds(320, 20, 200, 300); //Setting postiion of the panel inside the JPanel and setting width & height
        this.placementPanel.add(shipSelect);     



     makeShips(shipSelect);

  private void makeShips(JPanel inPanel)
  {
      System.out.println("make ships testing");
    this.shipButton[0] = new JButton("Aircraft Carrier");
    boardShips[0] = new Ship(5, "Aircraft Carrier", 0);

    this.shipButton[1] = new JButton("Battleship");
    boardShips[1] = new Ship(4, "Battleship", 1);

    this.shipButton[2] = new JButton("Cruiser");
  boardShips[2] = new Ship(3, "Cruiser", 2);

    this.shipButton[3] = new JButton("Destroyer 1");
    boardShips[3] = new Ship(2, "Destroyer", 3);


    this.shipButton[4] = new JButton("Submarine 1");
    boardShips[4] = new Ship(1, "Submarine", 4);

  System.out.println("make ships testing22");

    for (int i = 0; i < 5; i++)
    {
      this.shipButton[i].setName("" + i);
     this.shipButton[i].addActionListener((ActionListener) this);
      inPanel.add(this.shipButton[i]);
      this.boardShips[i].makeIcons();
    }

  }

AT SHIP CLASS：

  public Ship(int tempSize, String tempName, int tempButton)
  {
    this();
    this.size = tempSize;
    this.name = tempName;
    this.button = tempButton;
   // this.shipCoords = new int[this.size][2];
    //this.shipIcons = new ImageIcon[2][this.size];
    //this.shipSunkIcons = new ImageIcon[2][this.size];
  }

Answer 1

你有这个private JButton[] shipButton;，这是Jbutton数组没有在任何地方初始化，你正试图做this.shipButton[0] = new JButton("Aircraft Carrier"); causin NPE。

我看到你有5个shipButton数组

  JButton[] shipButton=new JButton[5];

修改

你不能从类体调用方法。你只能在那里定义方法。要调用您的方法，您必须使用构造函数或其他方法。

线程“main”中的异常java.lang.NullPointerException错误在Java

1 个答案: