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在Java中存在异常时将默认值分配给最终变量

final try-catch java

Alfonso · 技术社区 · 16 年前

为什么Java不允许在尝试块中设置值之后,在catch块中给最终变量赋值,即使在异常情况下不可能写入最终值。

下面是一个演示问题的示例:

public class FooBar {

    private final int foo;

    private FooBar() {
        try {
            int x = bla();
            foo = x; // In case of an exception this line is never reached
        } catch (Exception ex) {
            foo = 0; // But the compiler complains
                     // that foo might have been initialized
        }
    }

    private int bla() { // You can use any of the lines below, neither works
        // throw new RuntimeException();
        return 0;
    }
}

这个问题并不难解决,但我想理解为什么编译器不接受这个问题。

提前感谢您提供任何信息!

3 回复 | 直到 16 年前

danben 16 年前

try {
    int x = bla();
    foo = x; // In case of an exception this line is never reached
} catch (Exception ex) {
    foo = 0; // But the compiler complains
             // that foo might have been initialized
}

原因是编译器无法推断异常只能在 foo 是初始化的。这个例子是一个特殊情况,很明显这是正确的,但是要考虑:

try {
    int x = bla();
    foo = x; // In case of an exception this line is never reached...or is it?
    callAnotherFunctionThatThrowsAnException();  // Now what?
} catch (Exception ex) {
    foo = 0; // But the compiler complains
             // that foo might have been initialized,
             // and now it is correct.
}

编写一个编译器来处理这种非常具体的情况是一项艰巨的任务——很可能有很多这样的情况。