Not reachable code

[Kapil Sakhuja]

public class Test{
	
	public static void main(String[] sss){
		System.out.println("entered main...");
		fun();
		System.out.println("exiting main...");	// LINE 1: Shouldn't this line be 'not reachable'?
	}
	public static void fun(){
			throw new ArithmeticException();
			//System.out.println("inside fun..."); // LINE 2: compiler says this line is not reachable

	}	
}

In the code above, at line marked 'LINE 2' the compiler rightly says that the code is not reachable, but it doesn't report the same problem with line marked as 'LINE 1'. Why can't the compiler see that the function fun() has only one line of code and that code is just throwing an exception, which means that the line 'LINE 1' will never execute in this code.

[Astha Sharma]

Compiler is not intelligent enough to predict the exception inside function call. It can not get at compile time that fun() can throw an exception. Instead of function call if you write-

public static void main(String[] sss){  
        System.out.println("entered main...");  
        throw new ArithmeticException();  
        System.out.println("exiting main...");  
    }  

compiler will get the error in this case.

[Kapil Sakhuja]

Thanks Astha!

I tried to look at the JLS and this is what i could follow from the same: The compiler follows a process called as 'static analysis' and so it knows that 'only' in the case of break, continue, return or throw statement, the code cannot complete 'normally' and so any statement after one of these statements becomes not reachable. A function call is treated like other expressions, and so the compiler is not able to make out whether this call will complete normally or not.

[Astha Sharma]

oh...its interesting. thanks

[Seetharaman Venkatasamy]

Kapil Sakhuja wrote: The compiler follows a process called as 'static analysis' and so it knows that 'only' in the case of break, continue, return or throw statement, the code cannot complete 'normally' and so any statement after one of these statements becomes not reachable.

Plus, also with below kind of statement,

while(true){}
System.out.println("Error:Not Reachable Code");

[Astha Sharma]

Seetharaman Venkatasamy wrote:
Plus, also with below kind of statement,

while(true){}
System.out.println("Error:Not Reachable Code");

then why the following code generates no error?

boolean b;
while(b=true)
{}
System.out.println("hello");

[Matthew Brown]

Again, static analysis won't pick that up. b = true is an expression, not a compile-time constant. It happens to be an expression that always evaluates to true, but the compiler doesn't bother trying to work that out.

[Astha Sharma]

ok....thankyou