Question

Please help me answer these questions in java programming language. Please answer it line after line so that I can understand please.

Does it compile or not?
No programming is done in this exercise, simply answer the questions asked in the code given
below.

class Exemple {
/*Explain why this code does not compile
*/
public void m1() {
foo();
}
public int foo() throws Exception {
throw new Exception();
}
/*Explain why this code is not considered as good
*/
public void m2() {
try {
//do stuff...
} catch (Exception e) {
} }
/* Explain why this code does not compile
*/
public void m3() {
try {
//do stuff...

} catch (Exception e) {
} catch (NullPointerException e) {

} }

/* Explain why this code does not compile
*/
public void m4() {
throw new CustomCheckedException();
}
private class CustomCheckedException extends Exception {
private static final long serialVersionUID = -7944813576443065516L;
public CustomCheckedException() {
//nothing
} }
/* Explain why this code does not compile
*/
public int m5() {
int age;
String s = "24";
try {
age = getAccessCode();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
return age;
}
public int getAccessCode() throws IllegalAccessException {
throw new IllegalAccessException();
}
/* Explain why this code COMPILES */
public void m6() {
bar();
}
public int bar() {
throw new RuntimeException();
} }

Answer 1

class Exemple {
/*Explain why this code does not compile
* Ans : method foo() declars that it will throw Exception. so any method which calling foo()
* have to write it in try and catch block or it can declare throw Exception in method definition
* other wise it will throw compile time error
* so correct implementation is
* public void m1() throws Exception{
foo();
}
or
public void m1() {
try {
       foo();
   } catch (Exception e) {
       // TODO Auto-generated catch block
       e.printStackTrace();
   }
}
*/
public void m1() {
  
       foo();
  
}
public int foo() throws Exception {
   throw new Exception();
}
}

/*Explain why this code is not considered as good

Here Exception being caught is of type Exception. This is the parent of all Exceptions. There no way to find out exactly what type of exception is being caught here like IOException, SqlException. It reduces the readability of the program.
*/
public void m2() {
try {
//do stuff...
} catch (Exception e) {
} }

/* Explain why this code does not compile

Ans : In catch block , Exception is being caught first then NullPointerException. NullPointerException is sub-class of Exception class. The rule is sub-class Exception should be caught first then parent. that's why this program won't compile.
*/
public void m3() {
try {
//do stuff...

} catch } catch

(Exception e) { (NullPointerException e) {

} }

/* Explain why this code does not compile

Ans : There are two errors in this snnipet.

1. while declaring class only public, abstract & final are permitted. But here private given.

2. m4() throws new CustomCheckedException() exception, but neither it is adding try-catch or it is declaring CustomCheckedException using throws
*/
public void m4() {
throw new CustomCheckedException();
}
private class CustomCheckedException extends Exception {
private static final long serialVersionUID = -7944813576443065516L;
public CustomCheckedException() {
//nothing
} }

/* Explain why this code does not compile
   * Ans: Local must be initialized in java, before using it. Age here is not initialized thats' why this
   * error is coming.
   */
   public int m5() {
   int age;
   String s = "24";
   try {
   age = getAccessCode();
   } catch (IllegalAccessException e) {
   e.printStackTrace();
   }
   return age;
   }
   public int getAccessCode() throws IllegalAccessException {
   throw new IllegalAccessException();
   }

/* Explain why this code COMPILES
   * Ans: RuntimeException It is a system Exception.
   * it is not recoverable
   * So we don't write try-catch or throws
   * */
   public void m6() {
   bar();
   }
   public int bar() {
           throw new RuntimeException();
   }