??????3. ????????ü??????
ExceptionA??ExceptionB??ExceptionC
public class ExceptionA extends Exception {
public ExceptionA(String str) {
super();
}
}
public class ExceptionB extends ExceptionA {
public ExceptionB(String str) {
super(str);
}
}
public class ExceptionC extends ExceptionA {
public ExceptionC(String str) {
super(str);
}
}
????????????????
public class NeverCaught {
static void f() throws ExceptionB{
throw new ExceptionB("exception b");
}
static void g() throws ExceptionC {
try {
f();
} catch (ExceptionB e) {
ExceptionC c = new ExceptionC("exception a");
throw c;
}
}
public static void main(String[] args) {
try {
g();
} catch (ExceptionC e) {
e.printStackTrace();
}
}
}
/*
exception.ExceptionC
at exception.NeverCaught.g(NeverCaught.java:12)
at exception.NeverCaught.main(NeverCaught.java:19)
*/
??????????????????ExceptionC????д????ExceptionB???????????????????°?!
???????????????????????????????????????????з???????????????????????????????????????????????????????????????????????????????????????????????????
public class NeverCaught {
static void f() throws ExceptionB{
throw new ExceptionB("exception b");
}
static void g() throws ExceptionC {
try {
f();
} catch (ExceptionB e) {
ExceptionC c = new ExceptionC("exception a");
//????
c.initCause(e);
throw c;
}
}
public static void main(String[] args) {
try {
g();
} catch (ExceptionC e) {
e.printStackTrace();
}
}
}
/*
exception.ExceptionC
at exception.NeverCaught.g(NeverCaught.java:12)
at exception.NeverCaught.main(NeverCaught.java:21)
Caused by: exception.ExceptionB
at exception.NeverCaught.f(NeverCaught.java:5)
at exception.NeverCaught.g(NeverCaught.java:10)
... 1 more
*/
???????????????????????????????????????initCause()???????Throwable??е??
??????4. ???????
???????????????????????????????????????Щ??????????????????IO??JDBC??????????????????м??????????????????????????ζ?????й??????????????????????????????????????￡????????????????????????finally??
public void readFile(String file) {
BufferedReader reader = null;
try {
reader = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
// do some other work
} catch (FileNotFoundException e) {
e.printStackTrace();
} finally {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
?????????????????????????????????????????????JDBC?????????????????(??????????????????????????????????????????????????)
????Try…finally??????????????????????Ρ???????????????й????л???????????????????????????????????try?????”????”??????а?????????finally?н???????????????????????
public void readFile() {
BufferedReader reader = null;
try {
reader = new BufferedReader(new InputStreamReader(new FileInputStream("file")));
// do some other work
//close reader
reader.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
????????????????????????????????????????????????????????????????reader???????????????Υ???????reader.close()???????????????????????????????????κ???????????????????????????????????????????????(?????????????????????)??????????????try…finally??????
public void readFile() {
BufferedReader reader = null;
try {
try {
reader = new BufferedReader(new InputStreamReader(new FileInputStream("file")));
// do some other work
// close reader
} finally {
reader.close();
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
??????????????????????????????????????????????????????????????????try…finally???????????(??????鷳??java??????й??о?)??
???????????????????????????????д?????????????????JDBC????????????????????????????????????????????????????м?????????????????????????????????????????????????????????
public class ResourceInConstructor {
BufferedReader reader = null;
public ResourceInConstructor() {
try {
reader = new BufferedReader(new InputStreamReader(new FileInputStream("")));
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
public void readFile() {
try {
while(reader.readLine()!=null) {
//do some work
}
} catch (IOException e) {
e.printStackTrace();
}
}
public void dispose() {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
??????????????????????????????????????????????????????java?л????к???????????????