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三． 以finally進行清理
1. 如果某段代碼不管是否發生異常都要執行，那可把它改入finally塊中。
import java.sql.SQLException;
class TestException{
public static void tSql() throws SQLException {
System.out.println("Originating the exception in tSql()");
throw new SQLException("throw in tSql");
}
public void f() throws SQLException{
try{
tSql();
}
catch(SQLException ex){
System.out.println("catch SQLException in f()");
throw ex;//（1）
}
finally{
System.out.println("finally in f()");
}
}
}
public class Test{
public static void main(String[] args){
TestException te = new TestException();
try{
te.f();
}
catch(SQLException ex){
System.out.println("catch te.f() SQLException in main");
}
catch(Exception ex){
System.out.println("catch te.f() Exception in main");
}
}
}
運行結果為：
Originating the exception in tSql()
catch SQLException in f()
finally in f()
catch te.f() SQLException in main
雖然在代碼（1）處重新拋出異常，但finally塊中的代碼仍然會被執行。
2. finally造成的異常遺失
如果在finally中執行的代碼又產生異常，那么在上一層調用中所捕捉到的異常的起始拋出點會是finally所在的函數。
import java.sql.SQLException;
class TestException{
public static void tSql1() throws SQLException {
System.out.println("Originating the exception in tSql()");
throw new SQLException("throw in tSql1");
}
public static void tSql2() throws SQLException {
System.out.println("Originating the exception in tSql()");
throw new SQLException("throw in tSql2");
}
public void f() throws SQLException{
try{
tSql1();
}
catch(SQLException ex){
System.out.println("catch SQLException in f()");
throw ex;//（2）
}
finally{
System.out.println("finally in f()");
//tSql2();（1）
}
}
}
public class Test{
public static void main(String[] args){
TestException te = new TestException();
try{
te.f();
}
catch(SQLException ex){
System.out.println("catch te.f() SQLException in main");
System.out.println("getMessage：" + ex.getMessage());
System.out.println("printStackTrace：");
ex.printStackTrace();
}
}
}
運行結果為：
Originating the exception in tSql()
catch SQLException in f()
finally in f()
catch te.f() SQLException in main
getMessage：throw in tSql1
printStackTrace：
java.sql.SQLException: throw in tSql1
void TestException.tSql1()
Test.java:5
void TestException.f()
Test.java:13
void Test.main(java.lang.String[])
Test.java:29
從結果可以看出，在main()中能正確打印出所捕捉到的異常的起始拋出點。但如果去掉代碼（1）的注釋，結果將變為：
Originating the exception in tSql()
catch SQLException in f()
finally in f()
Originating the exception in tSql()
catch te.f() SQLException in main
getMessage：throw in tSql2
printStackTrace：
java.sql.SQLException: throw in tSql2
void TestException.tSql2()
Test.java:9
void TestException.f()
Test.java:21
void Test.main(java.lang.String[])
Test.java:29
從結果可以看出，在main()中捕捉到的異常是finally中產生的異常，代碼（2）中拋出的異常丟失了。
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