try块也可以有零个或一个finally块。 finally块总是与try块一起使用。
语法
finally块的语法是：
finally {
// Code for finally block
}
finally块以关键字finally开始，后面紧跟一个大括号和一个大括号。finally块的代码放在大括号内。
try，catch和finally块有两种可能的组合：try-catch-finally或try-finally。try块可以后跟零个或多个catch块。try块最多可以有一个finally块。try块必须有一个catch块和一个finally块或两者都有。try-catch-finally块的语法是：
try {
// Code for try block
}
catch(Exception1 e1) {
// Code for catch block
}
finally {
// Code for finally block
}
try-finally块的语法是：
try {
// Code for try block
}
finally {
// Code for finally block
}
无论在相关联的try块和/或catch块中发生什么，finally块中的代码都保证执行。所以，一般使用finally块来写清理代码。
例如，可能用来释放一些资源，如数据库连接的关闭，文件的关闭等，当完成它们时，必须释放。
在try-finally块允许实现这个逻辑。代码结构将如下所示：
try {
// Obtain and use some resources here
}
finally {
// Release the resources that were obtained in the try block
}
示例-1
下面的代码演示了finally块的使用。
public class Main {
public static void main(String[] args) {
int x = 10, y = 0, z = 0
try {
System.out.println("Before dividing x by y.")
z = x / y
System.out.println("After dividing x by y.")
} catch (ArithmeticException e) {
System.out.println("Inside catch block a.")
} finally {
System.out.println("Inside finally block a.")
}
try {
System.out.println("Before setting z to 2.")
z = 2
System.out.println("After setting z to 2.")
}
catch (Exception e) {
System.out.println("Inside catch block b.")
} finally {
System.out.println("Inside finally block b.")
}
try {
System.out.println("Inside try block c.")
}
finally {
System.out.println("Inside finally block c.")
}
try {
System.out.println("Before executing System.exit().")
System.exit(0)
System.out.println("After executing System.exit().")
} finally {
// This finally block will not be executed
// because application exits in try block
System.out.println("Inside finally block d.")
}
}
}
上面的代码生成以下结果。
Before dividing x by y.
Inside catch block a.
Inside finally block a.
Before setting z to 2.
After setting z to 2.
Inside finally block b.
Inside try block c.
Inside finally block c.
Before executing System.exit().
重新抛出一个异常
捕获的异常可以被重新抛出。
public class Main {
public static void main(String[] args) {
try {
m1()
} catch (MyException e) {
// Print the stack trace
e.printStackTrace()
}
}
public static void m1() throws MyException {
try {
m2()
} catch (MyException e) {
e.fillInStackTrace()
throw e
}
}
public static void m2() throws MyException {
throw new MyException("An error has occurred.")
}
}
class MyException extends Exception {
public MyException() {
super()
}
public MyException(String message) {
super(message)
}
public MyException(String message, Throwable cause) {
super(message, cause)
}
public MyException(Throwable cause) {
super(cause)
}
}
上面的代码生成以下结果。
MyException: An error has occurred.
at Main.m1(Main.java:14)
at Main.main(Main.java:4)