javassist.bytecode.analysis

Class Analyzer

java.lang.Object

javassist.bytecode.analysis.Analyzer

All Implemented Interfaces:

Opcode

public class Analyzer
extends java.lang.Object
implements Opcode

A data-flow analyzer that determines the type state of the stack and local variable table at every reachable instruction in a method. During analysis, bytecode verification is performed in a similar manner to that described in the JVM specification.

Example:

 // Method to analyze
 public Object doSomething(int x) {
     Number n;
     if (x < 5) {
        n = new Double(0);
     } else {
        n = new Long(0);
     }

     return n;
 }

 // Which compiles to:
 // 0:   iload_1
 // 1:   iconst_5
 // 2:   if_icmpge   17
 // 5:   new #18; //class java/lang/Double
 // 8:   dup
 // 9:   dconst_0
 // 10:  invokespecial   #44; //Method java/lang/Double."<init>":(D)V
 // 13:  astore_2
 // 14:  goto    26
 // 17:  new #16; //class java/lang/Long
 // 20:  dup
 // 21:  lconst_1
 // 22:  invokespecial   #47; //Method java/lang/Long."<init>":(J)V
 // 25:  astore_2
 // 26:  aload_2
 // 27:  areturn

 public void analyzeIt(CtClass clazz, MethodInfo method) {
     Analyzer analyzer = new Analyzer();
     Frame[] frames = analyzer.analyze(clazz, method);
     frames[0].getLocal(0).getCtClass(); // returns clazz;
     frames[0].getLocal(1).getCtClass(); // returns java.lang.String
     frames[1].peek(); // returns Type.INTEGER
     frames[27].peek().getCtClass(); // returns java.lang.Number
 }
 

Author:

Jason T. Greene

See Also:

FramePrinter

Field Summary

Fields inherited from interface javassist.bytecode.Opcode

AALOAD, AASTORE, ACONST_NULL, ALOAD, ALOAD_0, ALOAD_1, ALOAD_2, ALOAD_3, ANEWARRAY, ARETURN, ARRAYLENGTH, ASTORE, ASTORE_0, ASTORE_1, ASTORE_2, ASTORE_3, ATHROW, BALOAD, BASTORE, BIPUSH, CALOAD, CASTORE, CHECKCAST, D2F, D2I, D2L, DADD, DALOAD, DASTORE, DCMPG, DCMPL, DCONST_0, DCONST_1, DDIV, DLOAD, DLOAD_0, DLOAD_1, DLOAD_2, DLOAD_3, DMUL, DNEG, DREM, DRETURN, DSTORE, DSTORE_0, DSTORE_1, DSTORE_2, DSTORE_3, DSUB, DUP, DUP_X1, DUP_X2, DUP2, DUP2_X1, DUP2_X2, F2D, F2I, F2L, FADD, FALOAD, FASTORE, FCMPG, FCMPL, FCONST_0, FCONST_1, FCONST_2, FDIV, FLOAD, FLOAD_0, FLOAD_1, FLOAD_2, FLOAD_3, FMUL, FNEG, FREM, FRETURN, FSTORE, FSTORE_0, FSTORE_1, FSTORE_2, FSTORE_3, FSUB, GETFIELD, GETSTATIC, GOTO, GOTO_W, I2B, I2C, I2D, I2F, I2L, I2S, IADD, IALOAD, IAND, IASTORE, ICONST_0, ICONST_1, ICONST_2, ICONST_3, ICONST_4, ICONST_5, ICONST_M1, IDIV, IF_ACMPEQ, IF_ACMPNE, IF_ICMPEQ, IF_ICMPGE, IF_ICMPGT, IF_ICMPLE, IF_ICMPLT, IF_ICMPNE, IFEQ, IFGE, IFGT, IFLE, IFLT, IFNE, IFNONNULL, IFNULL, IINC, ILOAD, ILOAD_0, ILOAD_1, ILOAD_2, ILOAD_3, IMUL, INEG, INSTANCEOF, INVOKEDYNAMIC, INVOKEINTERFACE, INVOKESPECIAL, INVOKESTATIC, INVOKEVIRTUAL, IOR, IREM, IRETURN, ISHL, ISHR, ISTORE, ISTORE_0, ISTORE_1, ISTORE_2, ISTORE_3, ISUB, IUSHR, IXOR, JSR, JSR_W, L2D, L2F, L2I, LADD, LALOAD, LAND, LASTORE, LCMP, LCONST_0, LCONST_1, LDC, LDC_W, LDC2_W, LDIV, LLOAD, LLOAD_0, LLOAD_1, LLOAD_2, LLOAD_3, LMUL, LNEG, LOOKUPSWITCH, LOR, LREM, LRETURN, LSHL, LSHR, LSTORE, LSTORE_0, LSTORE_1, LSTORE_2, LSTORE_3, LSUB, LUSHR, LXOR, MONITORENTER, MONITOREXIT, MULTIANEWARRAY, NEW, NEWARRAY, NOP, POP, POP2, PUTFIELD, PUTSTATIC, RET, RETURN, SALOAD, SASTORE, SIPUSH, STACK_GROW, SWAP, T_BOOLEAN, T_BYTE, T_CHAR, T_DOUBLE, T_FLOAT, T_INT, T_LONG, T_SHORT, TABLESWITCH, WIDE

Constructor Summary

Constructors

Constructor and Description
Analyzer()

Method Summary

Modifier and Type	Method and Description
Frame[]	analyze(CtClass clazz, MethodInfo method) Performs data-flow analysis on a method and returns an array, indexed by instruction position, containing the starting frame state of all reachable instructions.
Frame[]	analyze(CtMethod method) Performs data-flow analysis on a method and returns an array, indexed by instruction position, containing the starting frame state of all reachable instructions.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Analyzer

public Analyzer()

Method Detail

analyze

public Frame[] analyze(CtClass clazz,
                       MethodInfo method)
                throws BadBytecode

Performs data-flow analysis on a method and returns an array, indexed by instruction position, containing the starting frame state of all reachable instructions. Non-reachable code, and illegal code offsets are represented as a null in the frame state array. This can be used to detect dead code. If the method does not contain code (it is either native or abstract), null is returned.

Parameters:

clazz - the declaring class of the method

method - the method to analyze

Returns:

an array, indexed by instruction position, of the starting frame state, or null if this method doesn't have code

Throws:

BadBytecode - if the bytecode does not comply with the JVM specification

analyze

public Frame[] analyze(CtMethod method)
                throws BadBytecode

Performs data-flow analysis on a method and returns an array, indexed by instruction position, containing the starting frame state of all reachable instructions. Non-reachable code, and illegal code offsets are represented as a null in the frame state array. This can be used to detect dead code. If the method does not contain code (it is either native or abstract), null is returned.

Parameters:

method - the method to analyze

Returns:

an array, indexed by instruction position, of the starting frame state, or null if this method doesn't have code

Throws:

BadBytecode - if the bytecode does not comply with the JVM specification