Question

我正在完成我的任务，在调用getfield操作时，我应该使用BCEL修改类文件来打印某些信息。
这包括如果引用字段的值大于30，则打印String 我遇到的问题是创建if条件目前我所拥有的是

instructionList.append(InstructionFactory.createDup(type.getSize()));
instructionList.append(new PUSH(constantPoolGen, 30));
instructionList.append(new ISUB());
instructionList.append(new IFGT(instructionList.append(instructionFactory.createPrintln("    !this value is greater than 30!"))));

第一行复制了getfield操作访问的值问题是对IFGT（）的调用。执行后我正在

Inconsistent stack height 2 != 3

我已经尝试打印ISUB结果并且正如预期的那样，用POP替换IFGT会使程序正常执行，这让我相信最后一行是问题。
字节码生成

Compiled from "Test.java"
public class Test extends java.lang.Object{
public Test();
  Code:
   0:   aload_0
   1:   invokespecial   #1; //Method java/lang/Object."<init>":()V
   4:   return

public static void main(java.lang.String[])   throws java.io.IOException;
  Code:
   0:   getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   3:   ldc     #3; //String Hello world
   5:   invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   8:   new     #5; //class Test$myobject
   11:  dup
   12:  invokespecial   #6; //Method Test$myobject."<init>":()V
   15:  astore_1
   16:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   19:  aload_1
   20:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   23:  ldc     #69; //String Before getfield:\n    Test$myobject\n    char\n    ftok
   25:  invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   28:  getfield        #7; //Field Test$myobject.ftok:C
   31:  ldc     #71; //String
   33:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   36:  dup_x1
   37:  pop
   38:  invokevirtual   #75; //Method java/io/PrintStream.print:(Ljava/lang/Object;)V
   41:  dup
   42:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   45:  dup_x1
   46:  pop
   47:  invokevirtual   #77; //Method java/io/PrintStream.print:(C)V
   50:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   53:  ldc     #79; //String
   55:  invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   58:  invokevirtual   #8; //Method java/io/PrintStream.println:(C)V
   61:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   64:  aload_1
   65:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   68:  ldc     #81; //String Before getfield:\n    Test$myobject\n    int\n    pok
   70:  invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   73:  getfield        #9; //Field Test$myobject.pok:I
   76:  ldc     #71; //String
   78:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   81:  dup_x1
   82:  pop
   83:  invokevirtual   #75; //Method java/io/PrintStream.print:(Ljava/lang/Object;)V
   86:  dup
   87:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   90:  dup_x1
   91:  pop
   92:  invokevirtual   #83; //Method java/io/PrintStream.print:(I)V
   95:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   98:  ldc     #79; //String
   100: invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   103: dup
   104: bipush  30
   106: isub
   107: getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   110: ldc     #85; //String     !this value is greater than 30!
   112: invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   115: ifgt    107
   118: invokevirtual   #10; //Method java/io/PrintStream.println:(I)V
   121: getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   124: aload_1
   125: getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   128: ldc     #87; //String Before getfield:\n    Test$myobject\n    int\n    pyk
   130: invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   133: getfield        #11; //Field Test$myobject.pyk:I
   136: ldc     #71; //String
   138: getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   141: dup_x1
   142: pop
   143: invokevirtual   #75; //Method java/io/PrintStream.print:(Ljava/lang/Object;)V
   146: dup
   147: getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   150: dup_x1
   151: pop
   152: invokevirtual   #83; //Method java/io/PrintStream.print:(I)V
   155: getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   158: ldc     #79; //String
   160: invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   163: dup
   164: bipush  30
   166: isub
   167: getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   170: ldc     #85; //String     !this value is greater than 30!
   172: invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   175: ifgt    167
   178: invokevirtual   #10; //Method java/io/PrintStream.println:(I)V
   181: iconst_5
   182: invokestatic    #12; //Method returnint:(I)I
   185: pop
   186: ldc     #13; //String plok
   188: invokestatic    #14; //Method returnstring:(Ljava/lang/String;)Ljava/lang/String;
   191: pop
   192: invokestatic    #15; //Method nothing:()V
   195: return

public static int returnint(int);
  Code:
   0:   getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   3:   iload_0
   4:   invokevirtual   #10; //Method java/io/PrintStream.println:(I)V
   7:   iload_0
   8:   ireturn

public static java.lang.String returnstring(java.lang.String);
  Code:
   0:   aload_0
   1:   areturn

public static void nothing();
  Code:
   0:   return

}

我尝试使用谷歌搜索答案但不幸的是我没有找到任何答案。

Java / BCEL堆栈高度不一致

0 个答案: