Java基础_try-catch-finally
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在处理异常的时候不是每次都把它 throws 掉就完事了,很多时候异常是需要我们自己来 catch 并针对所抛出的 Exception 做一些后续的处理工作。
直接上代码,先贴下面测试需要调用的方法:
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1. 抛出 Exception,没有 finally,当 catch 遇上 return
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后台输出结果:
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2. 抛出 Exception,当 catch 体里有 return,finally 体的代码块将在 catch 执行 return 之前被执行
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后台输出结果:
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3. 不抛 Exception,当 finally 代码块里面遇上 return,finally 执行完后将结束整个方法
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后台输出结果:
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4. 不抛 Exception,当 finally 代码块里面遇上 System.exit() 方法 将结束和终止整个程序,而不只是方法
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后台输出结果:
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5. 抛出 Exception,当 catch 和 finally 同时遇上 return,catch 的 return 返回值将不会被返回,finally 的 return 语句将结束整个方法并返回
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后台输出结果:
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6. 不抛出 Exception,当 finally 遇上 return,try 的 return 返回值将不会被返回,finally 的 return 语句将结束整个方法并返回
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后台输出结果:
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结语:
(假设方法需要返回值)
java 的异常处理中,在不抛出异常的情况下,程序执行完 try 里面的代码块之后,该方法并不会立即结束,而是继续试图去寻找该方法有没有 finally 的代码块:
1.如果没有 finally 代码块,整个方法在执行完 try 代码块后返回相应的值来结束整个方法;
2.如果有 finally 代码块,此时程序执行到 try 代码块里的 return 语句之时并不会立即执行 return,而是先去执行 finally 代码块里的代码,
2.1若 finally 代码块里没有 return 或没有能够终止程序的代码,程序将在执行完 finally 代码块代码之后再返回 try 代码块执行 return 语句来结束整个方法;
2.2若 finally 代码块里有 return 或含有能够终止程序的代码,方法将在执行完 finally 之后被结束,不再跳回 try 代码块执行 return。
在抛出异常的情况下,原理也是和上面的一样的,你把上面说到的 try 换成 catch 去理解就 OK。
转自:http://blog.csdn.net/lu_ca/article/details/52184423
结论:
1、不管有没有异常,finally中的代码都会执行
2、当try、catch中有return时,finally中的代码依然会继续执行
3、finally是在return后面的表达式运算之后执行的,此时并没有返回运算之后的值,而是把值保存起来,不管finally对该值做任何的改变,返回的值都不会改变,依然返回保存起来的值。也就是说方法的返回值是在finally运算之前就确定了的。
4、finally代码中最好不要包含return,程序会提前退出,也就是说返回的值不是try或catch中的值
举例:
情况1:try{}catch{}finally{} return;
程序正常进行
情况2:try{return;}catch{}finally{} return;
a、先执行try中的语句,包括return后面的表达式,b、然后执行finally中的语句,c、最后执行try中的return
ps:返回值是try中的return后面的表达式的值,finally后面的return语句不会被执行
情况3:try{} catch{return;} finally{} return;
先执行try中的代码块
有异常:a、先执行catch中的语句,包括return后面的表达式,b、然后执行finally中的语句,c、最后执行catch中的return,finally后面的return不会被执行
无异常:执行finally中的代码块,然后执行return语句
情况4:try{return;} catch{} finally{return;}
a、先执行try中的语句,包括return后面的表达式,b、然后执行finally中的语句,c、最后执行finally中的return
ps:返回的值是finally中return后面的表达式的值,因为finally中有return语句,所以会提前退出
情况5:try{} catch{return} finally{return};
先执行try中的代码块
有异常:a、先执行catch中的语句,包括return后面的表达式,b、然后执行finally中的语句,c、最后执行finally中的return,因为finally中有return语句,所以会提前退出
无异常:执行finally中的代码块,然后执行finally中的return
情况6:try{return;} catch{return;} finally{return;}
先执行try中的代码块,包括return后面的表达式
有异常:a、先执行catch中的语句,包括return后面的表达式,b、然后执行finally中的语句,c、最后执行finally中的return,因为finally中有return语句,所以会提前退出
无异常:执行finally中的代码块,然后执行finally中的return
最总结论:在执行try、catch中的return之前一定会执行finally中的代码(如果finally存在),如果finally中有return语句,就会直接执行finally中的return方法,所以finally中的return语句一定会被执行的。编译器把finally中的return语句标识为一个warning.
转自:https://www.cnblogs.com/hyzxx/p/5151911.html
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