add StringBuilder ; improve Object.toString

classes/java/lang/Object.java

@@ -8,7 +8,6 @@ public class Object {
     public native int hashCode();
 
     public String toString() {
-        return null;
-        //return getClass().getName() + "@" + Integer.toString(hashCode());
+        return getClass().getName() + "@" + Integer.toString(hashCode());
     }
 }

classes/java/lang/StringBuilder.java

@@ -0,0 +1,48 @@
+package java.lang;
+
+public class StringBuilder {
+    String[] strings;
+    int count;
+
+    public StringBuilder() {
+        strings = new String[0];
+    }
+
+    public StringBuilder(int capacity) {
+        strings = new String[capacity];
+    }
+
+    private void ensureCapacityInternal(int minimumCapacity) {
+        if (strings.length < minimumCapacity) {
+            String[] new_strings = new String[minimumCapacity + 3];
+            for (int i = 0; i < count; i++) {
+                new_strings[i] = strings[i];
+            }
+            strings = new_strings;
+        }
+    }
+
+    public StringBuilder append(String s) {
+        ensureCapacityInternal(count + 1);
+        strings[count] = s;
+        count += 1;
+        return this;
+    }
+
+    public String toString() {
+        int size = 0;
+        for (int i = 0; i < count; i++) {
+            size += strings[i].length();
+        }
+        byte[] buf = new byte[size];
+        int ix = 0;
+        for (int i = 0; i < count; i++) {
+            byte[] src = strings[i].getBytes();
+            for (int j = 0; j < src.length; j++) {
+                buf[ix] = src[j];
+                ix += 1;
+            }
+        }
+        return new String(buf);
+    }
+}

classes/test/TestClass.java

@@ -1,8 +1,17 @@
 package test;
 
 class TestClass {
-    public static void main() {
+    static void test1() {
         TestClass obj = new TestClass();
         System.out.println(obj.getClass().getName());
     }
+
+    static void test2() {
+        TestClass obj = new TestClass();
+        System.out.println(obj);
+    }
+
+    public static void main() {
+        test2();
+    }
 }