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--- teaching:labs:mdse:2013:bug_descriptions:jt-bug-cor111 [2013/11/25 15:44]
harshit.raikar
+++ teaching:labs:mdse:2013:bug_descriptions:jt-bug-cor111 [2018/05/09 01:59] (current)
@@ Line 1: / Line 1: @@
+====== Bug Cor 111 ======
+===== Inspired by =====
+  * [[http://findbugs.sourceforge.net/bugDescriptions.html#RV_RETURN_VALUE_IGNORED | RV_RETURN_VALUE_IGNORED]]
+===== Original Description =====
+"The return value of this method should be checked. One common cause of this warning is to invoke a method on an immutable object, thinking that it updates the object." -- 2013-10-14
+===== Detailed Description =====
+When a method that returns a result is invoked but the result is not used at the call site the programmer has likely not understood the method's behaviour.
+Often, she might expect that the method modifies the receiver object. However, that is not possible if the receiver object is immutable. Thus the method must return a modified copy of the object.
+In the scenario below, the programmer expects that the ''trim()'' method will update the String referenced by ''dateString''. But strings are immutable and thus the trim method returns a new string object, which is ignored in the following scenario.
+===== Sample Problem Scenario =====
+There is a problem whenever a method that returns a result is not part of an enclosing expression but used as a statement:
+<code Java>
+public class MethodIgnoresReturnValue {
+	static String date = "18/11/2013";
+ void StringOperation()
+	{
+		   String dateString = date;
+		   dateString.trim();
+	}
+}
+</Code>
+===== Sample Fix =====
+We can reassign the return value of the trim method to the ''dateString'' variable.
+<code Java>
+public class MethodIgnoresReturnValue {
+	static String date = "18/11/2013";
+ void StringOperation1()
+	{
+		   String dateString = date;
+		   dateString = dateString.trim();
+	}
+}
+</Code>
+===== Evaluation Results =====
+^  Benchmark project  ^  Precision              ^^^  Recall                ^^^
+|                     |  FB    |  JT    |  Delta  |  FB    |  JT    |  Delta |
+|  Project ...        |  ...%  |  ...%  |  ...%   |  ...%  |  ...%  |  ...%  |
+|  Project ...        |  ...%  |  ...%  |  ...%   |  ...%  |  ...%  |  ...%  |
+FB = FindBugs, JT = JTransformer, Delta = JTransformer - FindBugs

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