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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