added better support for methods, maxLocals and maxStack is now calculated (was dummy constant before). JavaOpcodes contains info about the number of pops/pushes and an indication of wide-ness (1 or 2 bytes for constantpool index)

src/main/java/nl/sander/beejava/CodeContainer.java

@@ -54,4 +54,6 @@ public abstract class CodeContainer {
         }
         this.owner = beeSource;
     }
+
+    public abstract boolean isConstructor();
 }

src/main/java/nl/sander/beejava/CompiledClass.java

@@ -40,7 +40,7 @@ public class CompiledClass {
         }
     }
 
-    Set<ConstantPoolEntry> getConstantTree() {
+    public Set<ConstantPoolEntry> getConstantTree() {
         return constantTree;
     }
 

src/main/java/nl/sander/beejava/Compiler.java

@@ -68,8 +68,7 @@ public class Compiler {
         this.codeAttributeNameEntry = constantPoolEntryCreator.getOrCreateUtf8("Code");
         compiledClass.addConstantPoolEntry(codeAttributeNameEntry);
 
-        ConstantPool constantPool = constantPoolCreator.createConstantPool(compiledClass.getConstantTree());
-        return constantPool;
+        return constantPoolCreator.createConstantPool(compiledClass.getConstantTree());
     }
 
     public void addConstructors() {
@@ -98,13 +97,15 @@ public class Compiler {
                 constantPoolEntryCreator.getOrCreateUtf8(method.getName()),
                 constantPoolEntryCreator.getOrCreateUtf8(method.getSignature()))
                 .addAccessFlags(method.getAccessFlags())
-                .addAttribute(MethodCodeCreator.createCodeAttribute(codeAttributeNameEntry, method.getCode()));
+                .addAttribute(MethodCodeCreator.createCodeAttribute(codeAttributeNameEntry, method));
     }
 
     /*
      * inspect a method or constructor, extract items that need to be added, and add them to the constant pool
      */
     private void updateConstantPool(CodeContainer codeContainer) {
+        compiledClass.addConstantPoolEntry(constantPoolEntryCreator.getOrCreateUtf8(codeContainer.getName()));
+        compiledClass.addConstantPoolEntry(constantPoolEntryCreator.getOrCreateUtf8(codeContainer.getSignature()));
         codeContainer.getCode().forEach(this::updateConstantPool);
     }
 

src/main/java/nl/sander/beejava/JavaOpcode.java

@@ -0,0 +1,40 @@
+package nl.sander.beejava;
+
+public enum JavaOpcode {
+    LDC(0x12, false, +1),
+    LDC_W(0x13,true, +1),
+    LDC2_W ( 0x14, true, +2),
+
+    ALOAD_0 ( 0x2a, false, +1),
+    RETURN ( 0xb1,false, 0),
+    GETSTATIC ( 0xb2,true, +1),
+    GETFIELD ( 0xb4,true, +1),
+
+    INVOKEINTERFACE ( 0xb5, true, -1),
+    INVOKEVIRTUAL ( 0xb6, true, -1),
+    INVOKESPECIAL ( 0xb7, true, -1),
+    INVOKESTATIC ( 0xb8, true, -1),
+    INVOKEDYNAMIC ( 0xba,true,-1);
+
+    private final int opcode;
+    private final boolean wide;
+    private final int stackDif;
+
+    JavaOpcode(int opcode, boolean wide, int stackDif) {
+        this.opcode=opcode;
+        this.wide=wide;
+        this.stackDif=stackDif;
+    }
+
+    public int getByteCode() {
+        return opcode;
+    }
+
+    public boolean isWide() {
+        return wide;
+    }
+
+    public int getStackDif() {
+        return stackDif;
+    }
+}

src/main/java/nl/sander/beejava/JavaOpcodes.java

@@ -1,19 +0,0 @@
-package nl.sander.beejava;
-
-public class JavaOpcodes {
-    public static final int LDC = 0x12;
-    public static final int LDC_W = 0x13;
-    public static final int LDC2_W = 0x14;
-
-    public static final int ALOAD_0 = 0x2a;
-    public static final int RETURN = 0xb1;
-    public static final int GETSTATIC = 0xb2;
-    public static final int GETFIELD = 0xb4;
-
-    public static final int INVOKEINTERFACE = 0xb5;
-    public static final int INVOKEVIRTUAL = 0xb6;
-    public static final int INVOKESPECIAL = 0xb7;
-    public static final int INVOKESTATIC = 0xb8;
-    public static final int INVOKEDYNAMIC = 0xba;
-
-}

src/main/java/nl/sander/beejava/MethodCodeCreator.java

@@ -3,26 +3,64 @@ package nl.sander.beejava;
 import nl.sander.beejava.api.CodeLine;
 import nl.sander.beejava.classinfo.attributes.CodeAttribute;
 import nl.sander.beejava.constantpool.entry.ConstantPoolEntry;
+import nl.sander.beejava.constantpool.entry.MethodRefEntry;
 import nl.sander.beejava.constantpool.entry.Utf8Entry;
 import nl.sander.beejava.util.ByteBuf;
 
-import java.util.List;
-
 public class MethodCodeCreator {
 
-    public static CodeAttribute createCodeAttribute(Utf8Entry codeAttributeNameEntry, List<CodeLine> code) {
+    public static CodeAttribute createCodeAttribute(Utf8Entry codeAttributeNameEntry, CodeContainer codeContainer) {
         CodeAttribute codeAttribute = new CodeAttribute(codeAttributeNameEntry);
-        codeAttribute.setMaxStack(1);
-        codeAttribute.setMaxLocals(1);
+        codeAttribute.setMaxStack(calculateMaxStack(codeContainer));
+        codeAttribute.setMaxLocals(codeContainer.formalParameters.size() + 1);
         ByteBuf byteBuf = new ByteBuf();
-        code.forEach(codeLine -> {
+
+        codeContainer.getCode().forEach(codeLine -> {
+            JavaOpcode javaOpcode = codeLine.getJavaOpcode(); // the opcode we determined in calculateMaxStack
+            byteBuf.addU8(javaOpcode.getByteCode());
             ConstantPoolEntry constantPoolEntry = codeLine.getAssignedEntry();
-            byteBuf.addU8(OpcodeMapper.mapOpcode(codeLine));
             if (constantPoolEntry != null) {
-                byteBuf.addU16(constantPoolEntry.getIndex());
+                if (javaOpcode.isWide()) {
+                    byteBuf.addU16(constantPoolEntry.getIndex());
+                } else if (constantPoolEntry.getIndex() < 0x100) {
+                    byteBuf.addU8(constantPoolEntry.getIndex());
+                } else {
+                    throw new IllegalStateException("cannot use non-wide opcode with wide constantpool index");
+                }
             }
         });
         codeAttribute.setCode(byteBuf.toBytes());
         return codeAttribute;
     }
+
+    private static int calculateMaxStack(CodeContainer codeContainer) {
+        int stackSize = 0;
+        int maxStackSize = 0;
+        for (CodeLine codeLine : codeContainer.getCode()) {
+            JavaOpcode javaOpcode = OpcodeMapper.mapOpcode(codeLine);
+            codeLine.setJavaOpcode(javaOpcode); //not really nice that we mutate codeLine, but this way we don't have to calculate the JavaOpcode twice
+            stackSize += javaOpcode.getStackDif();
+            ConstantPoolEntry assignedEntry = codeLine.getAssignedEntry();
+            if (assignedEntry instanceof MethodRefEntry) {
+                MethodRefEntry methodRefEntry = (MethodRefEntry) assignedEntry;
+                String argumentTypes = methodRefEntry.getNameAndType().getType();
+                stackSize -= getNrArguments(argumentTypes);
+            }
+            if (stackSize > maxStackSize) {
+                maxStackSize = stackSize;
+            }
+        }
+
+        return maxStackSize;
+    }
+
+    private static int getNrArguments(String argumentTypes) {
+        int nr = 0;
+        for (int i = 0; i < argumentTypes.length(); i++) {
+            if (argumentTypes.charAt(i) == ',') {
+                nr += 1;
+            }
+        }
+        return nr;
+    }
 }

src/main/java/nl/sander/beejava/OpcodeMapper.java

@@ -8,33 +8,33 @@ import nl.sander.beejava.flags.ClassAccessFlags;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 
-import static nl.sander.beejava.JavaOpcodes.*;
+import static nl.sander.beejava.JavaOpcode.*;
 
 public class OpcodeMapper {
 
-    public static int mapOpcode(CodeLine codeLine) {
+    public static JavaOpcode mapOpcode(CodeLine codeLine) {
         Opcode opcode = codeLine.getOpcode();
         return switch (opcode) {
             case GET -> isStatic(codeLine.getExternalfield()) ? GETSTATIC : GETFIELD;
             case LD_VAR -> ALOAD_0;
             case LD_CONST -> loadConst(codeLine);
             case INVOKE -> invoke(codeLine);
-            case RETURN -> JavaOpcodes.RETURN; //TODO not complete yet
-            default -> 0;
+            case RETURN -> JavaOpcode.RETURN; //TODO not complete yet
+            default -> throw new IllegalStateException("something not implemented");
         };
     }
 
     /* TODO cover more cases */
-    private static int invoke(CodeLine codeLine) {
+    private static JavaOpcode invoke(CodeLine codeLine) {
         BeeSource source = codeLine.getOwner().getOwner();
-        if (source.getAccessFlags().contains(ClassAccessFlags.SUPER)) {
+        if (source.getAccessFlags().contains(ClassAccessFlags.SUPER) && codeLine.getOwner().isConstructor()) {
             return INVOKESPECIAL;
         } else {
             return INVOKEVIRTUAL;
         }
     }
 
-    private static int loadConst(CodeLine codeLine) {
+    private static JavaOpcode loadConst(CodeLine codeLine) {
         Object constValue = codeLine.getConstValue();
         int index = codeLine.getAssignedEntry().getIndex();
         if (constValue instanceof Double || constValue instanceof Long) {

src/main/java/nl/sander/beejava/StackOp.java

@@ -0,0 +1,5 @@
+package nl.sander.beejava;
+
+public enum StackOp {
+    PUSH,POP
+}

src/main/java/nl/sander/beejava/api/BeeConstructor.java

@@ -38,6 +38,11 @@ public final class BeeConstructor extends CodeContainer {
         return Void.class;
     }
 
+    @Override
+    public boolean isConstructor() {
+        return true;
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

src/main/java/nl/sander/beejava/api/BeeMethod.java

@@ -37,6 +37,11 @@ public final class BeeMethod extends CodeContainer {
         return returnType;
     }
 
+    @Override
+    public boolean isConstructor() {
+        return false;
+    }
+
     public void validate() {
         //TODO
         /*

src/main/java/nl/sander/beejava/api/CodeLine.java

@@ -2,6 +2,7 @@ package nl.sander.beejava.api;
 
 
 import nl.sander.beejava.CodeContainer;
+import nl.sander.beejava.JavaOpcode;
 import nl.sander.beejava.TypeMapper;
 import nl.sander.beejava.constantpool.entry.ConstantPoolEntry;
 
@@ -22,11 +23,10 @@ public final class CodeLine {
     private String outputSignature;
     private BeeField ownfield; // when you create a class with a field, you can refer to it
     private Field externalfield; // when you refer to a field from another class
-
     private Object constValue;
-
     private ConstantPoolEntry assignedEntry;
     private CodeContainer owner;
+    private JavaOpcode javaOpcode;
 
     CodeLine(int linenumber, Opcode opcode) {
         this.linenumber = linenumber;
@@ -241,4 +241,12 @@ public final class CodeLine {
     public void setOwner(CodeContainer codeContainer) {
         this.owner = codeContainer;
     }
+
+    public JavaOpcode getJavaOpcode() {
+        return javaOpcode;
+    }
+
+    public void setJavaOpcode(JavaOpcode javaOpcode) {
+        this.javaOpcode = javaOpcode;
+    }
 }

src/main/java/nl/sander/beejava/constantpool/entry/MethodRefEntry.java

@@ -8,6 +8,7 @@ public class MethodRefEntry extends ConstantPoolEntry {
     private final ClassEntry classRef;
     private final NameAndTypeEntry nameAndType;
 
+
     public MethodRefEntry(ClassEntry classRef, NameAndTypeEntry nameAndType) {
         super(classRef, nameAndType);
         this.classRef = classRef;
@@ -22,6 +23,9 @@ public class MethodRefEntry extends ConstantPoolEntry {
         return nameAndType.getIndex();
     }
 
+    public NameAndTypeEntry getNameAndType() {
+        return nameAndType;
+    }
 
     public byte[] getBytes() {
         return new byte[]{TAG, upperByte(getClassIndex()), lowerByte(getClassIndex()), upperByte(getNameAndTypeIndex()), lowerByte(getNameAndTypeIndex())};

src/test/java/nl/sander/beejava/e2e/BeanWithMethodsTest.java

@@ -0,0 +1,48 @@
+package nl.sander.beejava.e2e;
+
+import nl.sander.beejava.BytecodeGenerator;
+import nl.sander.beejava.CompiledClass;
+import nl.sander.beejava.Compiler;
+import nl.sander.beejava.TestData;
+import nl.sander.beejava.api.BeeSource;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * A rather simple case, still meaningful nonetheless.
+ * Green means class can be loaded, so the class file structure is valid.
+ * The EmptyBean class just contains a default constructor.
+ */
+public class BeanWithMethodsTest {
+    @Test
+    public void testEmptyBean() throws Exception {
+        // Arrange
+        BeeSource emptyClass = TestData.createClassWithTwoReferencesToSomeClass();
+
+        // Act
+        CompiledClass compiledClass = Compiler.compile(emptyClass);
+        byte[] bytecode = BytecodeGenerator.generate(compiledClass);
+
+        ByteClassLoader classLoader = new ByteClassLoader();
+        classLoader.setByteCode("nl.sander.beejava.test.ClassWithReferences", bytecode);
+
+        // Assert
+        Class<?> classWithReferences = classLoader.loadClass("nl.sander.beejava.test.ClassWithReferences");
+        assertNotNull(classWithReferences);
+
+        Method[] methods = classWithReferences.getDeclaredMethods();
+        assertEquals(2, methods.length);
+        assertEquals("print1", methods[0].getName());
+        assertTrue(Modifier.isPublic(methods[0].getModifiers()));
+        assertEquals(0,methods[0].getParameterCount());
+
+        assertEquals("print2", methods[1].getName()); // ordering may cause failures
+        assertTrue(Modifier.isPublic(methods[1].getModifiers()));
+        assertEquals(0,methods[1].getParameterCount());
+
+    }
+}