what does Dead Code mean under Eclipse IDE Problems Section

Question

I am using Eclipse Helios IDE for our Web Application development. Under Problems section in Eclipse, for some of lines the description is displayed as "Dead Code".

Could anybody please tell me what does Dead Code actually mean ?

Please see the screen shot for your reference.

For example this part is shown as dead code under Eclipse

 else {         int length;         if (ar != null)             length = Array.getLength(ar);         else             length = 0; // This line is dead code 

Answer 1

In Eclipse, "dead code" is code that will never be executed. Usually it's in a conditional branch that logically will never be entered.

A trivial example would be the following:

boolean x = true; if (x) {    // do something } else {    // this is dead code! } 

It's not an error, because it's still valid java, but it's a useful warning, especially if the logical conditions are complex, and where it may not be intuitively obvious that the code will never be executed.

In your specific example, Eclipse has calculated that ar will always be non-null, and so the else length = 0 branch will never be executed.

And yes, it's possible that Eclipse is wrong, but it's much more likely that it's not.

Answer 2

Dead code is code that will never be executed, e.g.

 boolean b = true  if (!b) {     ....      // dead code here  }