java - try-catch 和 throws Exception 在性能上有什么区别？

Question

我知道在用法方面存在差异。但我想讨论性能差异。

BTW，《Effective Java》里面有一句话:

Placing code inside a try-catch block inhibits certain optimizations that modern JVM implementations might otherwise perform.

那么，如果有一个方法抛出异常，是否意味着这种优化不会应用到这个方法上？

Answer 1

为什么不在代码中尝试？

public class ExPerformanceTest {

    private int someVar = 0;
    private int iterations = 100000000;

    @Test
    public void throwTest() throws Exception {
        long t;
        t = System.currentTimeMillis();
        for (int i = 0; i < iterations; i++) {
            throwingMethod();
        }
        t = System.currentTimeMillis() - t;
        System.out.println("Throw Test took " + t + " ms");
    }

    @Test
    public void tryCatchTest() throws Exception {
        long t;
        t = System.currentTimeMillis();
        for (int i = 0; i < iterations; i++) {
            tryCatchMethod();
        }
        t = System.currentTimeMillis() - t;
        System.out.println("Try-Catch Test took " + t + " ms");
    }

    @Test
    public void anotherTryCatchTest() throws Exception {
        long t;
        t = System.currentTimeMillis();
        for (int i = 0; i < iterations; i++) {
            tryCatchMethodThatNeverEverThrows();
        }
        t = System.currentTimeMillis() - t;
        System.out.println("Try-Catch That Never Throws Test took " + t + " ms");
    }

    private void throwingMethod() throws Exception {
        // do some stuff here
        someVar++;
        willNeverThrow();
    }

    private void tryCatchMethod() {
        try {
            // do some stuff here
            someVar++;
            willNeverThrow();
        } catch (Exception e) {
            System.out.println("You shouldn't see this ever");
        }
    }

    private void tryCatchMethodThatNeverEverThrows() {
        try {
            // do some stuff here
            someVar++;
        } catch (Exception e) {
            System.out.println("You shouldn't see this ever");
        }
    }

    private void willNeverThrow() throws Exception {
        if (someVar == -1) {
            throw new RuntimeException("Shouldn't happen");
        }
    }
}

这给出了相当预期的数字:

运行 1

Try-Catch That Never Throws Test took 36 ms
Throw Test took 139 ms
Try-Catch Test took 160 ms

运行 2

Try-Catch That Never Throws Test took 26 ms
Throw Test took 109 ms
Try-Catch Test took 113 ms

运行 3

Try-Catch That Never Throws Test took 32 ms
Throw Test took 137 ms
Try-Catch Test took 194 ms

显然，JVM 发现 tryCatchMethodThatNeverEverThrows 实际上不需要 catch 部分并对其进行了优化，因此方法执行时间比其他方法少几倍。

在其他情况下，使用 catch 子句进行处理确实需要一些时间。