Basic tool for JVM bytecode generation written in Go
- Generate valid bytecode and Java classes
- Define classes, methods and global fields
- API for creating local variables
- Optimized constant pool generation
- Automatic locals calculation
- Java 6+ support (missing StackMapTable implementation)
- Automatic max stack calculation
- Labels support
package main
import (
"github.com/mikigal/bytecode"
)
func main() {
code := bytecode.CreateClass("Test", "java/lang/Object")
code.AddInterface("java/io/Serializable")
code.SourceFile("Test.java")
// Add two global fields
code.AddField(bytecode.Flag_Public | bytecode.Flag_Static | bytecode.Flag_Final, "firstNumber", "I", 5)
code.AddField(bytecode.Flag_Public | bytecode.Flag_Static | bytecode.Flag_Final, "secondNumber", "I", 10)
// Create main method
main := code.AddMainMethod(2)
localVar := main.AddLocalVar("test") // Define local String var
main.AddFieldInstruction(bytecode.Getstatic, "java/lang/System", "out", "Ljava/io/PrintStream;")
main.LoadLocalVar(localVar)
main.AddInvokeInstruction(bytecode.Invokevirtual, "java/io/PrintStream", "println", "(Ljava/lang/String;)V")
main.AddFieldInstruction(bytecode.Getstatic, "java/lang/System", "out", "Ljava/io/PrintStream;")
main.AddInvokeInstruction(bytecode.Invokestatic, "Test", "add", "()I")
main.AddInvokeInstruction(bytecode.Invokevirtual, "java/io/PrintStream", "println", "(I)V")
main.AddInstruction(bytecode.Return)
// Add second method
add := code.AddMethod(bytecode.Flag_Private | bytecode.Flag_Static, "add", "()I", 2)
add.AddFieldInstruction(bytecode.Getstatic, "Test", "firstNumber", "I")
add.AddFieldInstruction(bytecode.Getstatic, "Test", "secondNumber", "I")
add.AddInstruction(bytecode.Iadd)
add.AddInstruction(bytecode.Ireturn)
writeFile(code.ToBytes())
}public class Test implements java.io.Serializable
minor version: 0
major version: 49
flags: ACC_PUBLIC
Constant pool:
#1 = Utf8 Test
#2 = Class #1 // Test
#3 = Utf8 java/lang/Object
#4 = Class #3 // java/lang/Object
#5 = Utf8 java/io/Serializable
#6 = Class #5 // java/io/Serializable
#7 = Utf8 SourceFile
#8 = Utf8 Test.java
#9 = Utf8 firstNumber
#10 = Utf8 I
#11 = Utf8 ConstantValue
#12 = Integer 5
#13 = NameAndType #9:#10 // firstNumber:I
#14 = Fieldref #2.#13 // Test.firstNumber:I
#15 = Utf8 secondNumber
#16 = Integer 10
#17 = NameAndType #15:#10 // secondNumber:I
#18 = Fieldref #2.#17 // Test.secondNumber:I
#19 = Utf8 main
#20 = Utf8 ([Ljava/lang/String;)V
#21 = Utf8 Code
#22 = Utf8 test
#23 = String #22 // test
#24 = Utf8 java/lang/System
#25 = Class #24 // java/lang/System
#26 = Utf8 out
#27 = Utf8 Ljava/io/PrintStream;
#28 = NameAndType #26:#27 // out:Ljava/io/PrintStream;
#29 = Fieldref #25.#28 // java/lang/System.out:Ljava/io/PrintStream;
#30 = Utf8 java/io/PrintStream
#31 = Class #30 // java/io/PrintStream
#32 = Utf8 println
#33 = Utf8 (Ljava/lang/String;)V
#34 = NameAndType #32:#33 // println:(Ljava/lang/String;)V
#35 = Methodref #31.#34 // java/io/PrintStream.println:(Ljava/lang/String;)V
#36 = Utf8 add
#37 = Utf8 ()I
#38 = NameAndType #36:#37 // add:()I
#39 = Methodref #2.#38 // Test.add:()I
#40 = Utf8 (I)V
#41 = NameAndType #32:#40 // println:(I)V
#42 = Methodref #31.#41 // java/io/PrintStream.println:(I)V
{
public static final int firstNumber;
descriptor: I
flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL
ConstantValue: int 5
public static final int secondNumber;
descriptor: I
flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL
ConstantValue: int 10
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=2, args_size=1
0: ldc #23 // String test
2: astore_1
3: getstatic #29 // Field java/lang/System.out:Ljava/io/PrintStream;
6: aload_1
7: invokevirtual #35 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
10: getstatic #29 // Field java/lang/System.out:Ljava/io/PrintStream;
13: invokestatic #39 // Method add:()I
16: invokevirtual #42 // Method java/io/PrintStream.println:(I)V
19: return
private static int add();
descriptor: ()I
flags: ACC_PRIVATE, ACC_STATIC
Code:
stack=2, locals=0, args_size=0
0: getstatic #14 // Field firstNumber:I
3: getstatic #18 // Field secondNumber:I
6: iadd
7: ireturn
}
SourceFile: "Test.java"