diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/ByteBuffer.java b/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/ByteBuffer.java
index aa161983f..0f07a668c 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/ByteBuffer.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/ByteBuffer.java
@@ -54,6 +54,10 @@ public class ByteBuffer {
         return pos == end;
     }
 
+    public void skip(int count) {
+        pos += count;
+    }
+
     public byte get() {
         return data[pos++];
     }
diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/UTF16Helper.java b/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/UTF16Helper.java
index 163be31fd..29afb680e 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/UTF16Helper.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/UTF16Helper.java
@@ -34,7 +34,7 @@ public class UTF16Helper {
     }
 
     public static char lowSurrogate(int codePoint) {
-        return (char)(HIGH_SURROGATE_BITS | codePoint & SURROGATE_BIT_INV_MASK);
+        return (char)(LOW_SURROGATE_BITS | codePoint & SURROGATE_BIT_INV_MASK);
     }
 
     public static boolean isHighSurrogate(char c) {
diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/UTF8Charset.java b/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/UTF8Charset.java
index 55c7c2ec4..84e595d6a 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/UTF8Charset.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/impl/charset/UTF8Charset.java
@@ -53,6 +53,40 @@ public class UTF8Charset extends Charset {
 
     @Override
     public void decode(ByteBuffer source, CharBuffer dest) {
-
+        while (!source.end() && dest.available() >= 2) {
+            int b = source.get() & 0xFF;
+            if ((b & 0x80) == 0) {
+                dest.put((char)b);
+            } else if ((b & 0xE0) == 0xC0) {
+                if (source.end()) {
+                    dest.put((char)b);
+                    return;
+                }
+                dest.put((char)(((b & 0x1F) << 6) | (source.get() & 0x3F)));
+            } else if ((b & 0xF0) == 0xE0) {
+                if (source.available() < 2) {
+                    source.skip(source.available());
+                    dest.put((char)b);
+                    return;
+                }
+                byte b2 = source.get();
+                byte b3 = source.get();
+                char c = (char)(((b & 0x0F) << 12) | ((b2 & 0x3f) << 6) | (b3 & 0x3F));
+                dest.put(!UTF16Helper.isHighSurrogate(c) ? c : '?');
+            } else if ((b & 0xF8) == 0xF0) {
+                if (source.available() < 3) {
+                    source.skip(source.available());
+                    dest.put((char)b);
+                    return;
+                }
+                byte b2 = source.get();
+                byte b3 = source.get();
+                byte b4 = source.get();
+                int code = (((b & 0x07) << 18) | ((b2 & 0x3f) << 12) | ((b3 & 0x3F) << 6) | (b4 & 0x3F)) -
+                        UTF16Helper.SUPPLEMENTARY_PLANE;
+                dest.put(UTF16Helper.highSurrogate(code));
+                dest.put(UTF16Helper.lowSurrogate(code));
+            }
+        }
     }
 }
diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java
index 3a3056f10..61b1c1565 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java
@@ -46,7 +46,7 @@ class TAbstractStringBuilder extends TObject implements TSerializable, TCharSequ
     private static final int FLOAT_MAX_POS = 1000000;
     private static final long DOUBLE_MAX_POS = 1000000000000000L;
     char[] buffer;
-    int length;
+    private int length;
 
     public TAbstractStringBuilder() {
         this(16);
@@ -490,6 +490,11 @@ class TAbstractStringBuilder extends TObject implements TSerializable, TCharSequ
         return this;
     }
 
+    protected TAbstractStringBuilder append(TObject obj) {
+        append(TString.wrap(obj != null ? obj.toString() : "null"));
+        return this;
+    }
+
     private void ensureCapacity(int capacity) {
         if (buffer.length >= capacity) {
             return;
@@ -522,7 +527,7 @@ class TAbstractStringBuilder extends TObject implements TSerializable, TCharSequ
         return buffer[index];
     }
 
-    public TAbstractStringBuilder append(TCharSequence s, int start, int end) {
+    protected TAbstractStringBuilder append(TCharSequence s, int start, int end) {
         if (start > end || end > s.length() || start < 0) {
             throw new TIndexOutOfBoundsException();
         }
@@ -533,10 +538,19 @@ class TAbstractStringBuilder extends TObject implements TSerializable, TCharSequ
         return this;
     }
 
-    public TAbstractStringBuilder append(TCharSequence s) {
+    protected TAbstractStringBuilder append(TCharSequence s) {
         return append(s, 0, s.length());
     }
 
+    protected TAbstractStringBuilder append(char[] chars, int offset, int len) {
+        ensureCapacity(length + len);
+        len += offset;
+        while (offset < len) {
+            buffer[length++] = chars[offset++];
+        }
+        return this;
+    }
+
     @Override
     public TCharSequence subSequence(int start, int end) {
         // TODO: implement
diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TString.java b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
index d394b2b6a..576959afd 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
@@ -15,8 +15,12 @@
  */
 package org.teavm.classlib.java.lang;
 
+import org.teavm.classlib.impl.charset.ByteBuffer;
+import org.teavm.classlib.impl.charset.CharBuffer;
+import org.teavm.classlib.impl.charset.Charset;
 import org.teavm.classlib.impl.charset.UTF16Helper;
 import org.teavm.classlib.java.io.TSerializable;
+import org.teavm.classlib.java.io.TUnsupportedEncodingException;
 import org.teavm.javascript.ni.GeneratedBy;
 import org.teavm.javascript.ni.Rename;
 
@@ -24,8 +28,7 @@ import org.teavm.javascript.ni.Rename;
  *
  * @author Alexey Andreev <konsoletyper@gmail.com>
  */
-public class TString extends TObject implements TSerializable, TComparable<TString>,
-        TCharSequence {
+public class TString extends TObject implements TSerializable, TComparable<TString>, TCharSequence {
     private char[] characters;
     private transient int hashCode;
 
@@ -51,8 +54,43 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         }
     }
 
+    public TString(byte[] bytes, int offset, int length, TString charsetName) throws TUnsupportedEncodingException {
+        Charset charset = Charset.get(charsetName.toString());
+        if (charset == null) {
+            throw new TUnsupportedEncodingException(TString.wrap("Unknown encoding:" + charsetName));
+        }
+        initWithBytes(bytes, offset, length, charset);
+    }
+
+    public TString(byte[] bytes, int offset, int length) {
+        initWithBytes(bytes, offset, length, Charset.get("UTF-8"));
+    }
+
+    public TString(byte[] bytes) {
+        this(bytes, 0, bytes.length);
+    }
+
+    public TString(byte[] bytes, TString charsetName) throws TUnsupportedEncodingException {
+        this(bytes, 0, bytes.length, charsetName);
+    }
+
+    private void initWithBytes(byte[] bytes, int offset, int length, Charset charset) {
+        TStringBuilder sb = new TStringBuilder(bytes.length * 2);
+        this.characters = new char[sb.length()];
+        ByteBuffer source = new ByteBuffer(bytes, offset, offset + length);
+        char[] destChars = new char[TMath.max(8, TMath.min(length * 2, 1024))];
+        CharBuffer dest = new CharBuffer(destChars, 0, length * 2);
+        while (!source.end()) {
+            charset.decode(source, dest);
+            sb.append(destChars, 0, dest.position());
+            dest.rewind(0);
+        }
+        characters = new char[sb.length()];
+        sb.getChars(0, sb.length(), characters, 0);
+    }
+
     public TString(TStringBuilder sb) {
-        this(sb.buffer, 0, sb.length);
+        this(sb.buffer, 0, sb.length());
     }
 
     @Override
diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TStringBuilder.java b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TStringBuilder.java
index 8bcdd7e04..f3e0e8eee 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TStringBuilder.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TStringBuilder.java
@@ -20,6 +20,14 @@ package org.teavm.classlib.java.lang;
  * @author Alexey Andreev
  */
 public class TStringBuilder extends TAbstractStringBuilder {
+    public TStringBuilder(int capacity) {
+        super(capacity);
+    }
+
+    public TStringBuilder() {
+        super();
+    }
+
     @Override
     public TStringBuilder append(TString string) {
         super.append(string);
@@ -56,6 +64,12 @@ public class TStringBuilder extends TAbstractStringBuilder {
         return this;
     }
 
+    @Override
+    public TStringBuilder append(char[] chars, int offset, int len) {
+        super.append(chars, offset, len);
+        return this;
+    }
+
     @Override
     public TStringBuilder appendCodePoint(int codePoint) {
         super.appendCodePoint(codePoint);
@@ -73,4 +87,10 @@ public class TStringBuilder extends TAbstractStringBuilder {
         super.append(s);
         return this;
     }
+
+    @Override
+    public TStringBuilder append(TObject obj) {
+        super.append(obj);
+        return this;
+    }
 }
diff --git a/teavm-classlib/src/test/java/org/teavm/classlib/java/lang/StringTest.java b/teavm-classlib/src/test/java/org/teavm/classlib/java/lang/StringTest.java
index f23c6d6ce..351883f6a 100644
--- a/teavm-classlib/src/test/java/org/teavm/classlib/java/lang/StringTest.java
+++ b/teavm-classlib/src/test/java/org/teavm/classlib/java/lang/StringTest.java
@@ -16,6 +16,7 @@
 package org.teavm.classlib.java.lang;
 
 import static org.junit.Assert.*;
+import java.io.UnsupportedEncodingException;
 import org.junit.Test;
 
 /**
@@ -205,4 +206,16 @@ public class StringTest {
         assertEquals('2', array[1]);
         assertEquals('3', array[2]);
     }
+
+    @Test
+    public void createdFromByteArray() throws UnsupportedEncodingException {
+        byte[] bytes = { 49, 50, 51 };
+        assertEquals("123", new String(bytes, "UTF-8"));
+    }
+
+    @Test
+    public void createdFromUTF8ByteArray() throws UnsupportedEncodingException {
+        byte[] bytes = { 65, -62, -69, -32, -82, -69, -16, -66, -78, -69 };
+        assertEquals("A\u00BB\u0BBB\uD8BB\uDCBB", new String(bytes, "UTF-8"));
+    }
 }