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Java中finally和return的關(guān)系實例解析

更新時間：2018年02月01日 14:01:00 作者：司馬懿字仲達

這篇文章主要介紹了Java中finally和return的關(guān)系實例解析，總結(jié)了二者的關(guān)系，然后分享了相關(guān)代碼示例，小編覺得還是挺不錯的，具有一定借鑒價值，需要的朋友可以參考下

本文研究的主要是Java中finally和return的關(guān)系，具體介紹和實例如下所示。

finally 和 return 關(guān)系的總結(jié)

1.try塊中有System.exit(0)這樣的語句，由于它是終止Java虛擬機JVM的，連JVM都停止了，所有都結(jié)束了，當然finally語句也不會被執(zhí)行到。
2.其它情況下，finally語句都必然會被執(zhí)行。因此可以在這里執(zhí)行一些資源的釋放操作。

（1）finally中的return會覆蓋try/catch中的renturn。
（2）在finally中寫return語句會有警告，因為它會阻止函數(shù)拋出異常，而改為正常返回。

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語句是在try的return語句執(zhí)行之后，return返回之前執(zhí)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塊中包含了return語句，即使前面的catch塊重新拋出了異常，則調(diào)用該方法的語句也不會獲得catch塊重新拋出的異常，而是會得到finally塊的返回值，并且不會捕獲異常。
       */
			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塊中包含了return語句，即使前面的catch塊重新拋出了異常，則調(diào)用該方法的語句也不會獲得catch塊重新拋出的異常，而是會得到finally塊的返回值，并且不會捕獲異常。
       */
			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);是終止Java虛擬機JVM的，連JVM都停止了，所有都結(jié)束了，當然finally語句也不會被執(zhí)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();
	}
}

演示結(jié)果：