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POunboxing using the ASM Java library
 

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    <p>I'm using the ASM Java library to replace some reflection. I generate the body of this method:</p> <pre><code>void set(Object object, int fieldIndex, Object value); </code></pre> <p>With this generated method, I can set fields on an object at runtime without using reflection. It works great. However, I found it fails for primitive fields. Here is the relevant part of my set method:</p> <pre><code>for (int i = 0, n = cachedFields.length; i &lt; n; i++) { mv.visitLabel(labels[i]); mv.visitFrame(Opcodes.F_SAME, 0, null, 0, null); mv.visitVarInsn(ALOAD, 1); mv.visitTypeInsn(CHECKCAST, targetClassName); mv.visitVarInsn(ALOAD, 3); Field field = cachedFields[i].field; Type fieldType = Type.getType(field.getType()); mv.visitFieldInsn(PUTFIELD, targetClassName, field.getName(), fieldType.getDescriptor()); mv.visitInsn(RETURN); } </code></pre> <p>This code is generating case labels for a select. It works great for objects but for primitives I get this error:</p> <blockquote> <p>Expecting to find float on stack</p> </blockquote> <p>Ok, that makes sense, I need to do the unboxing myself. I implemented the following:</p> <pre><code>for (int i = 0, n = cachedFields.length; i &lt; n; i++) { mv.visitLabel(labels[i]); mv.visitFrame(Opcodes.F_SAME, 0, null, 0, null); mv.visitVarInsn(ALOAD, 1); mv.visitTypeInsn(CHECKCAST, targetClassName); mv.visitVarInsn(ALOAD, 3); Field field = cachedFields[i].field; Type fieldType = Type.getType(field.getType()); switch (fieldType.getSort()) { case Type.BOOLEAN: mv.visitTypeInsn(CHECKCAST, "java/lang/Boolean"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Boolean", "booleanValue", "()Z"); break; case Type.BYTE: mv.visitTypeInsn(CHECKCAST, "java/lang/Byte"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Byte", "byteValue", "()B"); break; case Type.CHAR: mv.visitTypeInsn(CHECKCAST, "java/lang/Character"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Character", "charValue", "()C"); break; case Type.SHORT: mv.visitTypeInsn(CHECKCAST, "java/lang/Short"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Short", "shortValue", "()S"); break; case Type.INT: mv.visitTypeInsn(CHECKCAST, "java/lang/Integer"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Integer", "intValue", "()I"); break; case Type.FLOAT: mv.visitTypeInsn(CHECKCAST, "java/lang/Float"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Float", "floatValue", "()F"); break; case Type.LONG: mv.visitTypeInsn(CHECKCAST, "java/lang/Long"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Long", "longValue", "()J"); break; case Type.DOUBLE: mv.visitTypeInsn(CHECKCAST, "java/lang/Double"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Double", "doubleValue", "()D"); break; case Type.ARRAY: mv.visitTypeInsn(CHECKCAST, fieldType.getDescriptor()); break; case Type.OBJECT: mv.visitTypeInsn(CHECKCAST, fieldType.getInternalName()); break; } mv.visitFieldInsn(PUTFIELD, targetClassName, field.getName(), fieldType.getDescriptor()); mv.visitInsn(RETURN); } </code></pre> <p>I have traced through and it definitely goes into "case Type.FLOAT" for the appropriate field, however, I get this error:</p> <blockquote> <p>Expecting to find object/array on stack</p> </blockquote> <p>This is where I'm stuck. For the life of me I can't figure out why the unboxing doesn't work. The "ALOAD, 3" is putting the third parameter of the set method on the stack, which should be a Float. Any ideas?</p> <p>I found the asm-commons library has a GeneratorAdapter class that has an unbox method. However, I don't really want to include yet another JAR for something that should be so simple. I looked at the GeneratorAdapter source and it is doing something very similar. I tried to modify my code to use GeneratorAdapter, just to see if it worked, but didn't find it at all easy to convert.</p>
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