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Useless Boxing

OPAL's standard bytecode representation provides an API that offers extensive support for pattern matching on Java bytecode. This greatly facilitates writing analyses that identify typical code smells.

For example, let's write an analysis to find instances of the following issue:

double value = 1.0d;
//...
int i = (new Double(value)).intValue // << the issue
//Intended: int i = (int) value

I.e., let's find code where we wrap a primitive value and immediately unwrap it. (Such code generally hinders comprehensibility and wastes CPU cycles; a real instance can be found in the OpenJDK 8.)

The complete(!) analysis to find the described bug pattern is shown next.

import org.opalj.br._
import org.opalj.br.instructions._
import org.opalj.br.reader.Java8Framework.ClassFiles

val project = ClassFiles(new java.io.File("/Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home/jre/lib"))

val theMethods = Set(
	"booleanValue","byteValue","charValue","shortValue",
	"intValue","longValue","floatValue","doubleValue")
for {
    (classFile,_) <- project.par // for all classes (let's do it in parallel)
    method @ MethodWithBody(body) <- classFile.methods // for all non-abstract, non-native methods
    pc <- body.matchPair { // find a sequence of two instructions where...
        case (
            INVOKESPECIAL(receiver1, _, _, TheArgument(parameterType: BaseType)),
            INVOKEVIRTUAL(receiver2, name, NoArgumentMethodDescriptor(returnType: BaseType))
            ) => { (receiver1 eq receiver2) &&
                   receiver1.isPrimitiveTypeWrapper &&
                   theMethods.contains(name) }
        case _ => false
    }
} println (classFile.fqn +"{"+ method.toJava+"::"+ body.lineNumber(pc)+"}")

You can paste the analysis in the Scala REPL to directly execute it. In this case, you'll get – for the OpenJDK 8 – the following result:

com/sun/org/apache/xalan/internal/lib/ExsltMath{double constant(java.lang.String,double)::Some(379)}

On a notebook (Core i7, 2,3 GHz, 8GB, SSD) loading the JDK takes 2 to 3 seconds, the analysis itself takes roughly 0.04 seconds for the entire JDK.