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
public boolean visit(Assignment node) {
			fSideEffectNodes.add(node);
			return false;
		}
		public boolean visit(MethodInvocation node) {
			fSideEffectNodes.add(node);
			return false;
		}		
		public boolean visit(ClassInstanceCreation node) {
			fSideEffectNodes.add(node);
			return false;
		}
		public boolean visit(SuperMethodInvocation node) {
			fSideEffectNodes.add(node);
			return false;
		}		
	}
	private SimpleName fName;
	public RemoveDeclarationCorrectionProposal(ICompilationUnit cu, SimpleName name, int relevance) {
		super("", cu, null, relevance, JavaPlugin.getDefault().getWorkbench().getSharedImages().getImage(ISharedImages.IMG_TOOL_DELETE)); 
		fName= name;
	}
	public String getDisplayString() {
		IBinding binding= fName.resolveBinding();
		String name= fName.getIdentifier();
		switch (binding.getKind()) {
			case IBinding.TYPE:
				return CorrectionMessages.getFormattedString("RemoveDeclarationCorrectionProposal.removeunusedtype.description", name); 
			case IBinding.METHOD:
				if (((IMethodBinding) binding).isConstructor()) {