考虑到这段代码,我能绝对确定finally块总是执行的吗,不管something()是什么?
try {
something();
return success;
}
catch (Exception e) {
return failure;
}
finally {
System.out.println("I don't know if this will get printed out");
}
考虑到这段代码,我能绝对确定finally块总是执行的吗,不管something()是什么?
try {
something();
return success;
}
catch (Exception e) {
return failure;
}
finally {
System.out.println("I don't know if this will get printed out");
}
当前回答
考虑以下程序:
public class SomeTest {
private static StringBuilder sb = new StringBuilder();
public static void main(String args[]) {
System.out.println(someString());
System.out.println("---AGAIN---");
System.out.println(someString());
System.out.println("---PRINT THE RESULT---");
System.out.println(sb.toString());
}
private static String someString() {
try {
sb.append("-abc-");
return sb.toString();
} finally {
sb.append("xyz");
}
}
}
从Java 1.8.162开始,上述代码块提供以下输出:
-abc-
---AGAIN---
-abc-xyz-abc-
---PRINT THE RESULT---
-abc-xyz-abc-xyz
这意味着使用finally释放对象是一种很好的做法,如以下代码所示:
private static String someString() {
StringBuilder sb = new StringBuilder();
try {
sb.append("abc");
return sb.toString();
} finally {
sb = null; // Just an example, but you can close streams or DB connections this way.
}
}
其他回答
是的,会的。无论try或catch块中发生什么,除非调用System.exit()或JVM崩溃。如果块中有任何return语句,finally将在该return语句之前执行。
示例代码:
public static void main(String[] args) {
System.out.println(Test.test());
}
public static int test() {
try {
return 0;
}
finally {
System.out.println("something is printed");
}
}
输出:
something is printed.
0
如果在嵌套的finally块中引发异常,finally也可以提前退出。编译器会警告你finally块没有正常完成,或者给出一个错误,说明你有无法访问的代码。仅当抛出不在条件语句后面或循环内部时,才会显示不可访问代码的错误。
try{
}finally{
try{
}finally{
//if(someCondition) --> no error because of unreachable code
throw new RunTimeException();
}
int a = 5;//unreachable code
}
下面是凯文的回答。重要的是要知道,要返回的表达式在finally之前求值,即使在finally之后返回。
public static void main(String[] args) {
System.out.println(Test.test());
}
public static int printX() {
System.out.println("X");
return 0;
}
public static int test() {
try {
return printX();
}
finally {
System.out.println("finally trumps return... sort of");
return 42;
}
}
输出:
X
finally trumps return... sort of
42
除了最后替换try块中的返回之外,异常也是如此。引发异常的finally块将替换try块中引发的返回或异常。