Java中finally和return的关系实例解析

• Z时代
• 2024-01-10
• 分类：综合

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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