当无法分配变量时,可能已经分配了变量

Question

研究这段代码:

public class TestFinalAndCatch {
    private final int i;

    TestFinalAndCatch(String[] args) {
        try {
            i = method1();
        } catch (IOException ex) {
            i = 0;  // error: variable i might already have been assigned
        }
    }

    static int method1() throws IOException {
        return 1;
    }
}

编译器说 java: variable i might already have been assigned

但对我来说,这似乎是不可能的情况.

Answer 1

i是最终的,因此只能分配一次.编译器可能不够聪明,无法实现如果抛出异常,则不会发生第一个赋值,如果不抛出异常,则不会发生第二个赋值.

Answer 2

问题在于,在这种情况下,编译器基于语法而不是基于语义的.有2个解决方法:第一个基于移动异常句柄的方法:

package com.java.se.stackoverflow;

public class TestFinalAndCatch {
    private final int i;

    TestFinalAndCatch(String[] args) {
        i = method1();
    }

    static int method1() {
        try {
            return 1;
        } catch (Exception ex) {
            return 0;
        }
    }
}

二,使用temporar变量:

package com.java.se.stackoverflow;

import java.io.IOException;

public class TestFinalAndCatch {
    private final int i;

    TestFinalAndCatch(String[] args) {
        int tempI;
        try {
            tempI = method1();
        } catch (IOException ex) {
            tempI = 0;
        }
        i = tempI;
    }

    static int method1() throws IOException {
        return 1;
    }
}