diff --git a/java/src/main/java/org/msgpack/object/ArrayType.java b/java/src/main/java/org/msgpack/object/ArrayType.java
index 694f53f0..350ce32e 100644
--- a/java/src/main/java/org/msgpack/object/ArrayType.java
+++ b/java/src/main/java/org/msgpack/object/ArrayType.java
@@ -60,6 +60,11 @@ public class ArrayType extends MessagePackObject {
 		return Arrays.equals(((ArrayType)obj).array, array);
 	}
 
+	@Override
+	public int hashCode() {
+		return array.hashCode();
+	}
+
 	@Override
 	public Object clone() {
 		MessagePackObject[] copy = new MessagePackObject[array.length];
diff --git a/java/src/main/java/org/msgpack/object/BigIntegerTypeIMPL.java b/java/src/main/java/org/msgpack/object/BigIntegerTypeIMPL.java
index f7c73ae1..fd517e70 100644
--- a/java/src/main/java/org/msgpack/object/BigIntegerTypeIMPL.java
+++ b/java/src/main/java/org/msgpack/object/BigIntegerTypeIMPL.java
@@ -103,6 +103,11 @@ class BigIntegerTypeIMPL extends IntegerType {
 		return ((BigIntegerTypeIMPL)obj).value.equals(value);
 	}
 
+	@Override
+	public int hashCode() {
+		return value.hashCode();
+	}
+
 	@Override
 	public Object clone() {
 		return new BigIntegerTypeIMPL(value);
diff --git a/java/src/main/java/org/msgpack/object/BooleanType.java b/java/src/main/java/org/msgpack/object/BooleanType.java
index c6e4f300..1d12c1ce 100644
--- a/java/src/main/java/org/msgpack/object/BooleanType.java
+++ b/java/src/main/java/org/msgpack/object/BooleanType.java
@@ -50,6 +50,15 @@ public class BooleanType extends MessagePackObject {
 		return ((BooleanType)obj).value == value;
 	}
 
+	@Override
+	public int hashCode() {
+		if(value) {
+			return 1231;
+		} else {
+			return 1237;
+		}
+	}
+
 	@Override
 	public Object clone() {
 		return new BooleanType(value);
diff --git a/java/src/main/java/org/msgpack/object/DoubleTypeIMPL.java b/java/src/main/java/org/msgpack/object/DoubleTypeIMPL.java
index dafe5405..b47a7096 100644
--- a/java/src/main/java/org/msgpack/object/DoubleTypeIMPL.java
+++ b/java/src/main/java/org/msgpack/object/DoubleTypeIMPL.java
@@ -82,6 +82,12 @@ class DoubleTypeIMPL extends FloatType {
 		return ((DoubleTypeIMPL)obj).value == value;
 	}
 
+	@Override
+	public int hashCode() {
+		long v = Double.doubleToLongBits(value);
+		return (int)(v^(v>>>32));
+	}
+
 	@Override
 	public Object clone() {
 		return new DoubleTypeIMPL(value);
diff --git a/java/src/main/java/org/msgpack/object/FloatTypeIMPL.java b/java/src/main/java/org/msgpack/object/FloatTypeIMPL.java
index 234b2ad9..1d799611 100644
--- a/java/src/main/java/org/msgpack/object/FloatTypeIMPL.java
+++ b/java/src/main/java/org/msgpack/object/FloatTypeIMPL.java
@@ -81,6 +81,11 @@ class FloatTypeIMPL extends FloatType {
 		return ((FloatTypeIMPL)obj).value == value;
 	}
 
+	@Override
+	public int hashCode() {
+		return Float.floatToIntBits(value);
+	}
+
 	@Override
 	public Object clone() {
 		return new FloatTypeIMPL(value);
diff --git a/java/src/main/java/org/msgpack/object/LongIntegerTypeIMPL.java b/java/src/main/java/org/msgpack/object/LongIntegerTypeIMPL.java
index 0ce22a25..940ab6fa 100644
--- a/java/src/main/java/org/msgpack/object/LongIntegerTypeIMPL.java
+++ b/java/src/main/java/org/msgpack/object/LongIntegerTypeIMPL.java
@@ -100,6 +100,11 @@ class LongIntegerTypeIMPL extends IntegerType {
 		return ((LongIntegerTypeIMPL)obj).value == value;
 	}
 
+	@Override
+	public int hashCode() {
+		return (int)(value^(value>>>32));
+	}
+
 	@Override
 	public Object clone() {
 		return new LongIntegerTypeIMPL(value);
diff --git a/java/src/main/java/org/msgpack/object/MapType.java b/java/src/main/java/org/msgpack/object/MapType.java
index d456e78f..619d3887 100644
--- a/java/src/main/java/org/msgpack/object/MapType.java
+++ b/java/src/main/java/org/msgpack/object/MapType.java
@@ -63,6 +63,11 @@ public class MapType extends MessagePackObject {
 		return Arrays.equals(((MapType)obj).map, map);
 	}
 
+	@Override
+	public int hashCode() {
+		return map.hashCode();
+	}
+
 	@Override
 	public Object clone() {
 		MessagePackObject[] copy = new MessagePackObject[map.length];
diff --git a/java/src/main/java/org/msgpack/object/NilType.java b/java/src/main/java/org/msgpack/object/NilType.java
index 7a463764..ece62f0a 100644
--- a/java/src/main/java/org/msgpack/object/NilType.java
+++ b/java/src/main/java/org/msgpack/object/NilType.java
@@ -39,6 +39,11 @@ public class NilType extends MessagePackObject {
 		return true;
 	}
 
+	@Override
+	public int hashCode() {
+		return 0;
+	}
+
 	@Override
 	public Object clone() {
 		return new NilType();
diff --git a/java/src/main/java/org/msgpack/object/RawType.java b/java/src/main/java/org/msgpack/object/RawType.java
index 18a419d1..3a394862 100644
--- a/java/src/main/java/org/msgpack/object/RawType.java
+++ b/java/src/main/java/org/msgpack/object/RawType.java
@@ -61,6 +61,11 @@ public class RawType extends MessagePackObject {
 		return ((RawType)obj).bytes.equals(bytes);
 	}
 
+	@Override
+	public int hashCode() {
+		return bytes.hashCode();
+	}
+
 	@Override
 	public Object clone() {
 		return new RawType((byte[])bytes.clone());
diff --git a/java/src/main/java/org/msgpack/object/ShortIntegerTypeIMPL.java b/java/src/main/java/org/msgpack/object/ShortIntegerTypeIMPL.java
index 83a4daf6..60e92b8e 100644
--- a/java/src/main/java/org/msgpack/object/ShortIntegerTypeIMPL.java
+++ b/java/src/main/java/org/msgpack/object/ShortIntegerTypeIMPL.java
@@ -102,6 +102,11 @@ class ShortIntegerTypeIMPL extends IntegerType {
 		return ((ShortIntegerTypeIMPL)obj).value == value;
 	}
 
+	@Override
+	public int hashCode() {
+		return value;
+	}
+
 	@Override
 	public Object clone() {
 		return new ShortIntegerTypeIMPL(value);