Question

我是Java的新手，无法弄清楚为什么我的if语句中的布尔值不能传递到下面的System.out.println(aa + " " + bb + " " + gate);。目标是在if语句中设置布尔值 aa 和 bb 的值，然后将两个变量传递到另一个带calculate(aa, bb);的方法。从每个if语句返回正确的值，但不是从System.out.println(aa + " " + bb + " " + gate);返回。如何保存两个布尔值并将其传递给其他内容？

 JButton btnCalculate = new JButton("Calculate");
    btnCalculate.addActionListener(new ActionListener() {
        JFrame error = new JFrame();
        public void actionPerformed(ActionEvent arg0) {
         try {
            int a = Integer.parseInt(textInputA.getText());
            int b = Integer.parseInt(textInputB.getText());
            String gate = String.valueOf(comboBoxGateSelect.getSelectedItem());
            if(a == 1) {
                boolean aa = true;
                System.out.println("a is " + aa + "(1)");
            }
            if(a == 0) {
                boolean aa = false;
                System.out.println("a is " + aa + "(0)");
            }
            if(b == 1) {
                boolean bb = true;
                System.out.println("b is " + bb + "(1)");
            }
            if(b == 0) {
                boolean bb = false;
                System.out.println("b is " + bb + "(0)");
            }
            if(a > 1 || a < 0) {
                JOptionPane.showMessageDialog(error, "Input A must be either 1 or 0. \r\n True = 1, False = 0.", "Error", JOptionPane.ERROR_MESSAGE, null);
            }
            if(b > 1 || b < 0) {
                JOptionPane.showMessageDialog(error, "Input B must be either 1 or 0. \r\n True = 1, False = 0.", "Error", JOptionPane.ERROR_MESSAGE, null);
            }
            System.out.println(a + " " + b + " " + gate);
            System.out.println(aa + " " + bb + " " + gate); // This one +
            calculate(aa, bb); // This one.
         } catch(NumberFormatException e) {
             JOptionPane.showMessageDialog(error, "Inputs A and B must be either 1 or 0. \r\n True = 1, False = 0.", "Error", JOptionPane.ERROR_MESSAGE, null);
         }      

        }
    });
    btnCalculate.setBackground(Color.GRAY);
    btnCalculate.setFont(new Font("Arial", Font.BOLD, 11));
    btnCalculate.setForeground(Color.BLACK);
    btnCalculate.setBounds(72, 204, 89, 23);
    contentPane.add(btnCalculate);

Answer 1

在if语句，循环或带括号{}的任何内容中声明的变量在这些括号内只能。要访问if语句之外的变量，请按以下方式声明：

boolean aa;    
if(a == 1) {     
aa = true;           
   System.out.println("a is " + aa + "(1)");
}

Answer 2

if语句，while循环等内部调用的所有变量只能通过括号内的命令访问。您必须在括号之前声明变量，如下所示：

boolean myBool;
if (true) {
    myBool = true;
} else {
    myBool = false;
}

希望这有帮助！

Java布尔值未传递出if语句

2 个答案: