Eclipse java dead code warning not working properly -

i using eclipse luna 4.4 think not showing me warning dead code.

it shows error

if(false){ // shows warning dead code here system.out.println("dead code"); } 

but doesn't show warning if say

boolean b = false; if(b){ // doesn't show warning dead code here system.out.println("dead code"); } 

somehow have little memory giving warning on previous version don't know which.

once doing like

boolean b = false; // code here // forgot make true in case if(b){// things here}  // gave me warning. 

do know happend here or there setting in preferences can this. thank in advance.