Question

我一直致力于为计算机科学项目创建周期表。我正在尝试编写一个创建按钮数组的代码。这些按钮上的文本是通过检索其他数组中按钮对应元素的名称来确定的。完成此操作后，根据它的元素类型，按钮会相应地着色。该程序编译良好，但它不运行。这是我的代码：

BufferedReader reader = null;
ElementsTest[] element = new ElementsTest[40];

      try {
           File file = new File("Elements 41-80.txt");
           reader = new BufferedReader(new FileReader(file));

           for (int counter = 0 ; counter < 40 ; counter++)
           {
                String name = reader.readLine();
                int atomicNum = counter + 1;
                String atomicWeight = reader.readLine();
                String elementSymbol = reader.readLine();
                String elementCharge = reader.readLine();
                String fullElectronConfig = reader.readLine();
                String shortElectronConfig = reader.readLine();
                String elementState = reader.readLine();
                String elementType = reader.readLine();
                String density = reader.readLine();
                String meltingPoint = reader.readLine();
                String boilingPoint = reader.readLine();
                String emptyLine = reader.readLine();

                element[counter] = new ElementsTest (name, atomicNum,  atomicWeight,       elementSymbol, elementCharge, fullElectronConfig, shortElectronConfig, elementState, elementType, density, meltingPoint, boilingPoint);
           }

      } catch (IOException e) {
           e.printStackTrace();
      }             

JButton[] buttonArray = new JButton[40];

      for (int counter2 = 0 ; counter2 < 40 ; counter2++)
      {
           String currentSymbol = element[counter2].getElementSymbol();
           buttonArray[counter2].setText(currentSymbol);

           if (element[counter2].getElementType().equals("Metal"))
           {
               buttonArray[counter2].setBackground(Color.ORANGE);
               buttonArray[counter2].setOpaque(true);
               buttonArray[counter2].setBorderPainted(false);
           }

           if (element[counter2].getElementType().equals("Non-Metal"))
           {
                buttonArray[counter2].setBackground(Color.GRAY);
                buttonArray[counter2].setOpaque(true);
                buttonArray[counter2].setBorderPainted(false);
           }

           if (element[counter2].getElementType().equals("Noble Gas"))
           {
                buttonArray[counter2].setBackground(Color.BLACK);
                buttonArray[counter2].setOpaque(true);
                buttonArray[counter2].setBorderPainted(false);
           }

           if (element[counter2].getElementType().equals("Transition Metal"))
           {
                buttonArray[counter2].setBackground(Color.GREEN);
                buttonArray[counter2].setOpaque(true);
                buttonArray[counter2].setBorderPainted(false);
           }

           if (element[counter2].getElementType().equals("Lanthanide"))
           {
                buttonArray[counter2].setBackground(Color.YELLOW);
                buttonArray[counter2].setOpaque(true);
                buttonArray[counter2].setBorderPainted(false);
           }

           if (element[counter2].getElementType().equals("Alkali Metal"))
           {
                buttonArray[counter2].setBackground(Color.RED);
                buttonArray[counter2].setOpaque(true);
                buttonArray[counter2].setBorderPainted(false);
           }

           if (element[counter2].getElementType().equals("Alkaline Earth Metal"))
           {
                buttonArray[counter2].setBackground(Color.BLUE);
                buttonArray[counter2].setOpaque(true);
                buttonArray[counter2].setBorderPainted(false);
           }

           if (element[counter2].getElementType().equals("Halogen"))
           {
                buttonArray[counter2].setBackground(Color.MAGENTA);
                buttonArray[counter2].setOpaque(true);
                buttonArray[counter2].setBorderPainted(false);
           }

           else {
                buttonArray[counter2].setOpaque(true);
           }
      }

按下RUN后出现此错误：

java.lang.NullPointerException
    at TestLayout.main(TestLayout.java:136)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at     edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:272)

有什么建议吗？

Answer 1

JButton[] buttonArray = new JButton[40];

这会创建一个空的按钮数组，这意味着每个元素都是null。首先需要通过将每个元素设置为new JButton()之类来填充数组，然后设置其属性。

Answer 2

你想：

JButton[i] = new JButton();

此代码创建一个新的jbutton数组JButton[i]

尝试在JButton上设置文本时java.lang.NullPointerException

2 个答案: