Implement more bytecode instructions

Author: ExcaliburZero

classes/IntBox.class

@@ -0,0 +1,11 @@
+public class IntBox {
+    private int value;
+
+    public IntBox(int value) {
+        this.value = value;
+    }
+
+    public int getValue() {
+        return this.value;
+    }
+}

classes/IntBox.java

@@ -1,11 +1,19 @@
+const ILOAD_1: u8 = 27;
 const ALOAD_0: u8 = 42;
+const IRETURN: u8 = 172;
 const RETURN: u8 = 177;
+const GETFIELD: u8 = 180;
+const PUTFIELD: u8 = 181;
 const INVOKESPECIAL: u8 = 183;
 
 #[derive(Debug)]
 pub enum Bytecode {
+    Iload_1,
     Aload_0,
+    Ireturn,
     Return,
+    Getfield(u16),
+    Putfield(u16),
     Invokespecial(u16),
 }
 
@@ -20,16 +28,44 @@ impl Bytecode {
             let instruction = bytes[i];
 
             match instruction {
+                ILOAD_1 => {
+                    bytecode.push((i, Iload_1));
+
+                    i += 1;
+                },
                 ALOAD_0 => {
                     bytecode.push((i, Aload_0));
 
                     i += 1;
                 },
+                IRETURN => {
+                    bytecode.push((i, Ireturn));
+
+                    i += 1;
+                },
                 RETURN => {
                     bytecode.push((i, Return));
 
                     i += 1;
                 },
+                GETFIELD => {
+                    let field = u16::from_be_bytes(
+                        [bytes[i + 1], bytes[i + 2]]
+                    );
+
+                    bytecode.push((i, Getfield(field)));
+
+                    i += 3;
+                },
+                PUTFIELD => {
+                    let field = u16::from_be_bytes(
+                        [bytes[i + 1], bytes[i + 2]]
+                    );
+
+                    bytecode.push((i, Putfield(field)));
+
+                    i += 3;
+                },
                 INVOKESPECIAL => {
                     let method = u16::from_be_bytes(
                         [bytes[i + 1], bytes[i + 2]]
@@ -52,9 +88,13 @@ impl ToString for Bytecode {
         use Bytecode::*;
 
         match self {
+            Iload_1 => "iload_1".to_string(),
             Aload_0 => "aload_0".to_string(),
+            Ireturn => "ireturn".to_string(),
             Return => "return".to_string(),
-            Invokespecial(method) => format!("invokespecial #{}", method),
+            Getfield(field) => format!("{:13} #{}", "getfield", field),
+            Putfield(field) => format!("{:13} #{}", "putfield", field),
+            Invokespecial(method) => format!("{:13} #{}", "invokespecial", method),
             _ => panic!(),
         }
     }