Back OCAJP
For the sake of OCAJP test, we need to remember this exception extending relationship, and which one should and have to be catch.
A runtime exception or unchecked exception is the RuntimeException class and its subclasses. It is ok for a program to catch it, but it is not a requirement.
Checked exception is the subclass of Exception but not subclass of RuntimeException. The program have to catch it.
Error is subclass of Error, program should not catch it.
OCAJP>cat test.java
import java.util.*;
class test {
public static void main(String...args) {
test t = new test();
t.tester(args[0]);
}
public void tester(String a) {
try{
switch(a) {
case "1":
throw new RuntimeException();
case "2":
throw new Exception();
case "3":
throw new Error();
case "4":
throw new Throwable();
default:
//throw new Object(); //error: incompatible types: Object cannot be converted to Throwable
}
} catch(RuntimeException r) {
System.out.println("optional");
} catch(Exception ex) {
System.out.println("mandantory, otherwise won't compile");
} catch(Error e) {
System.out.println("should not, but a valid syntax");
} catch(Throwable t) {
System.out.println("can catch Throwable, a valid syntax");
}
switch(a) {
case "1":
throw new RuntimeException("something bad will happen at run time, however, you can ignore it during compile");
case "2":
//throw new Exception("something you can not ignor"); //error: unreported exception Exception; must be caught or declared to be thrown
case "3":
throw new Error("fatal error beyond fix, don't catch it, should let the program fail");
case "4":
//throw new Throwable("It can be anything bad, not sure what it is"); //error: unreported exception Throwable; must be caught or declared to be thrown
default:
}
}
}
OCAJP>javac test.java
OCAJP>java test
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at test.main(test.java:5)
OCAJP>java test 1
optional
Exception in thread "main" java.lang.RuntimeException: something bad will happen at run time, however, you can ignore it during compile
at test.tester(test.java:32)
at test.main(test.java:5)
OCAJP>java test 2
mandantory, otherwise won't compile
Exception in thread "main" java.lang.Error: fatal error beyond fix, don't catch it, should let the program fail
at test.tester(test.java:36)
at test.main(test.java:5)
OCAJP>java test 3
should not, but a valid syntax
Exception in thread "main" java.lang.Error: fatal error beyond fix, don't catch it, should let the program fail
at test.tester(test.java:36)
at test.main(test.java:5)
OCAJP>java test 4
can catch Throwable, a valid syntax
OCAJP>java test 5
OCAJP>
Back OCAJP
