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
if (name.resolveBinding() == binding) {
						return curr;
					}
				}
			}
		}
		return null;
	}
	
	
	/**
	 * Remove the field or variable declaration including the initializer.
	 * 
	 */
	private void removeVariableReferences(ASTRewrite rewrite, SimpleName reference) {
		int nameParentType= reference.getParent().getNodeType();
		if (nameParentType == ASTNode.ASSIGNMENT) {
			Assignment assignment= (Assignment) reference.getParent();
			Expression rightHand= assignment.getRightHandSide();
			
			ASTNode parent= assignment.getParent();
			if (parent.getNodeType() == ASTNode.EXPRESSION_STATEMENT && rightHand.getNodeType() != ASTNode.ASSIGNMENT) {
				removeVariableWithInitializer(rewrite, rightHand, parent);
			}	else {
				rewrite.markAsReplaced(assignment, rewrite.createCopy(rightHand));
			}
		} else if (nameParentType == ASTNode.SINGLE_VARIABLE_DECLARATION) {
			rewrite.markAsRemoved(reference.getParent());
		} else if (nameParentType == ASTNode.VARIABLE_DECLARATION_FRAGMENT) {
			VariableDeclarationFragment frag= (VariableDeclarationFragment) reference.getParent();