为什么我会收到不可转换的类型错误？

Question

如果我使用这个类:

public class BooleanTest {
    public static void main(String args[]) {
        final Object[] objarray = new Object[2];
        try {
            objarray[0] = "Hello World!";
            objarray[1] = false;
        } catch (NullPointerException e) {
        }
        boolean bool = (boolean) objarray[1];
    }
}

它工作正常,我可以分配boolean没问题.在询问用户密码时,为什么我不能做同样的事情？

final Object result[] = new Object[2];
try {
    java.awt.EventQueue.invokeAndWait(new Runnable() {
        @Override
        public void run() {
            JPanel panel = new JPanel();
            panel.setLayout(new GridLayout(3,0));
            JLabel label = new JLabel();

            label.setHorizontalAlignment(SwingConstants.LEADING);
            JTextField input = new JTextField();

            input.setHorizontalAlignment(SwingConstants.CENTER);
            JCheckBox checkbox = new JCheckBox("Pair with this device");
            checkbox.setHorizontalAlignment(SwingConstants.LEADING);
            panel.add(label);
            panel.add(input);
            panel.add(checkbox);
            if (wrong) {
                label.setText("Wrong password. Please enter the password from the other device:");
            } else {
                label.setText("Please enter the password from the other device:");
            }
            int response = JOptionPane.showConfirmDialog(SendGUI.this, panel, "Enter password", JOptionPane.OK_CANCEL_OPTION);
            if (response == JOptionPane.OK_OPTION) {
                result[0] = input.getText();
                result[1] = (boolean)checkbox.isSelected();
            } else {
                result[0] = null;
                result[1] = false;
            }
        }
    });
} catch (InterruptedException e) {
} catch (InvocationTargetException e) {
}
boolean pair = (boolean)result[1]; //inconvertible type, expected boolean found Object

据我所知,我在两种情况下都做同样的事情,但第一个例子编译得很好而第二个例子没有.

Answer 1

您正在使用不同的编译器选项.你一定是.这两段代码都是在Java 7规则下编译的; 既不编译Java 6规则.例如,拿你的第一段代码(你说的编译代码):

c:\Users\Jon\Test>javac -source 1.7 BooleanTest.java

(No console output, i.e. no errors)

c:\Users\Jon\Test>javac -source 1.6 BooleanTest.java
warning: [options] bootstrap class path not set in conjunction with -source 1.6
BooleanTest.java:10: error: inconvertible types
        boolean bool = (boolean) objarray[1];
                                         ^
  required: boolean
  found:    Object
1 error
1 warning

编辑:我认为更改是在JLS(转换转换)的第5.5节中.

在Java 7的版本包括:

转换上下文允许使用以下之一:

• ...
• 缩小的引用转换(第5.1.6节),可选地后面是取消装箱转换(第5.1.8节)或未经检查的转换(第5.1.9节)

所述JLS第三版(爪哇5和6,基本上)包括:

转换上下文允许使用以下之一:

• ...
• 缩小的引用转换(第5.1.6节),可选地后跟未经检查的转换

请注意那里缺少"拆箱转换".