Java中finally和return的关系实例解析

本文研究的主要是Java中finally和return的关系，具体介绍和实例如下所示。

finally 和 return 关系的总结

1.try块中有System.exit(0)这样的语句，由于它是终止Java虚拟机JVM的，连JVM都停止了，所有都结束了，当然finally语句也不会被执行到。
2.其它情况下，finally语句都必然会被执行。因此可以在这里执行一些资源的释放操作。

（1）finally中的return会覆盖try/catch中的renturn。
（2）在finally中写return语句会有警告，因为它会阻止函数抛出异常，而改为正常返回。

package com.demo.test;public class FinallyAndReturn {private static void finallyAndTryReturn() {try {System.out.println("finallyAndTryReturn -> try");return;}catch (Exception e) {System.out.println("finallyAndTryReturn -> catch");}finally {System.out.println("finallyAndTryReturn -> finally");}}private static void finallyAndCatchReturn() {try {System.out.println("finallyAndCatchReturn -> try");throw new Exception();}catch (Exception e) {System.out.println("finallyAndCatchReturn -> catch");return;}finally {System.out.println("finallyAndCatchReturn -> finally");}}// finally语句是在try的return语句执行之后，return返回之前执行。private static String tryReturn() {String str = "initialized";try {System.out.println("tryReturn -> try");str = "try";return str;}catch (Exception e) {System.out.println("tryReturn -> catch");str = "catch";}finally {System.out.println("tryReturn -> finally");str = "finally";}return null;}private static String tryReturnAndFinallyReturn() {String str = "initialized";try {System.out.println("tryReturnAndFinallyReturn -> try");str = "try";return str;}catch (Exception e) {System.out.println("tryReturnAndFinallyReturn -> catch");str = "catch";}finally {System.out.println("tryReturnAndFinallyReturn -> finally");/*       * Warning: finally block does not complete normally       * 如果finally块中包含了return语句，即使前面的catch块重新抛出了异常，则调用该方法的语句也不会获得catch块重新抛出的异常，而是会得到finally块的返回值，并且不会捕获异常。       */str = "finally";return str;}}private static String tryThrowAndFinallyReturn() throws Exception {String str = "initialized";try {System.out.println("tryThrowAndFinallyReturn -> try");str = "try";throw new Exception();}catch (Exception e) {System.out.println("tryThrowAndFinallyReturn -> catch");str = "catch";throw new Exception();}finally {System.out.println("tryThrowAndFinallyReturn -> finally");/*       * Warning: finally block does not complete normally       * 如果finally块中包含了return语句，即使前面的catch块重新抛出了异常，则调用该方法的语句也不会获得catch块重新抛出的异常，而是会得到finally块的返回值，并且不会捕获异常。       */str = "finally";return str;}}private static void finallyAndRuntimeException() {try {System.out.println("finallyAndRuntimeException -> try");throw new RuntimeException();}catch (Exception e) {System.out.println("finallyAndRuntimeException -> catch");}finally {System.out.println("finallyAndRuntimeException -> finally");}}private static void finallyAndExit() {try {System.out.println("finallyAndExit -> try");// System.exit(0);是终止Java虚拟机JVM的，连JVM都停止了，所有都结束了，当然finally语句也不会被执行到。System.exit(0);}catch (Exception e) {System.out.println("finallyAndExit -> catch");}finally {System.out.println("finallyAndExit -> finally");}}public static void main(String[] args) {finallyAndTryReturn();System.out.println();finallyAndCatchReturn();System.out.println();System.out.println("tryReturn return -> " + tryReturn());System.out.println();System.out.println("tryReturnAndFinallyReturn return -> " + tryReturnAndFinallyReturn());System.out.println();try {System.out.println("tryThrowAndFinallyReturn return -> " + tryThrowAndFinallyReturn());}catch (Exception e) {e.printStackTrace();}System.out.println();finallyAndRuntimeException();System.out.println();finallyAndExit();}}

演示结果：

总结

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