Bug 50574 quick fix for removing local variable that is never read changes side effects
You'll need to set the "Local variable is never read" option in Window>Preferences>Java>Compiler>Unused Code to something other than "Ignore" to reproduce this. The quick fix "Remove variable <variable name> and assignments without possible side effects" that is offered if a local variable is never read makes two types of mistakes: 1. Some side effects are not recognized, e.g. "fixing" int k = 3; int n; n = k++; System.out.println (k); yields int k = 3; System.out.println (k); 2. The variable definition is removed even if it has side effects, e.g. int n = System.in.read (); is removed, whereas if a later assignment has side effects, it is left unchanged, including the now undefined reference to the local variable, e.g. int n; n = System.in.read (); becomes n = System.in.read (); What I think *should* happen is that the initializing assignment and later assignments should be treated alike; the left-hand side referring to the local variable should *always* be removed, and the right-hand side should be removed if and only if it has no side effects. This may result in invalid code if the right-hand side expression has side effects but does not form a statement; a deluxe version might extract the parts that have side effects and insert them as statements in the correct order, but even without this there would be a significant improvement over the current behaviour, which changes side effects and leaves references to undefined variables around.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/text/correction/RemoveDeclarationCorrectionProposal.java
ASTNode varDecl= frag.getParent();
			List fragments;
			if (varDecl instanceof VariableDeclarationExpression) {
				fragments= ((VariableDeclarationExpression) varDecl).fragments();
			} else if (varDecl instanceof FieldDeclaration) {
				fragments= ((FieldDeclaration) varDecl).fragments();
			} else {	
				fragments= ((VariableDeclarationStatement) varDecl).fragments();
			}
			if (fragments.size() == 1) {
				rewrite.markAsRemoved(varDecl);
			} else {
				rewrite.markAsRemoved(frag); 
			}
		}
	}
	
	private void removeVariableWithInitializer(ASTRewrite rewrite, ASTNode initializerNode, ASTNode statementNode) {
		ArrayList sideEffectNodes= new ArrayList();
		initializerNode.accept(new SideEffectFinder(sideEffectNodes));
		int nSideEffects= sideEffectNodes.size();
		if (nSideEffects == 0) {
			rewrite.markAsRemoved(statementNode); 
		} else {
			
		}
	}		
	
}