diff --git a/build.gradle b/build.gradle
index d38838f..58baa2e 100644
--- a/build.gradle
+++ b/build.gradle
@@ -2,11 +2,11 @@ apply plugin: 'java'
 apply plugin: 'jacoco'
 apply plugin: 'eclipse'
 
-sourceCompatibility = 1.7
+sourceCompatibility = 1.6
 
 group = 'org.beyene'
 archivesBaseName = 'sius'
-version = '0.2.0-SNAPSHOT'
+version = '0.3.0'
 
 sourceSets {
     main {
diff --git a/build.gradle.deploy b/build.gradle.deploy
index f0efe4d..06d4229 100644
--- a/build.gradle.deploy
+++ b/build.gradle.deploy
@@ -4,11 +4,11 @@ apply plugin: 'eclipse'
 apply plugin: 'maven'
 apply plugin: 'signing'
 
-sourceCompatibility = 1.7
+sourceCompatibility = 1.6
 
 group = 'org.beyene'
 archivesBaseName = 'sius'
-version = '0.2.0-SNAPSHOT'
+version = '0.3.0'
 
 sourceSets {
     main {
diff --git a/pom.xml b/pom.xml
index bf9c942..e4d9be2 100644
--- a/pom.xml
+++ b/pom.xml
@@ -3,7 +3,7 @@
 	<modelVersion>4.0.0</modelVersion>
 	<groupId>org.beyene</groupId>
 	<artifactId>sius</artifactId>
-	<version>0.2.0-SNAPSHOT</version>
+	<version>0.3.0</version>
 	<packaging>jar</packaging>
 	<name>${project.groupId}:${project.artifactId}</name>
 	<description>S.I. Unit System Conversion Library</description>
@@ -12,6 +12,7 @@
 	<properties>
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
+		<java.version>1.6</java.version>
 	</properties>
 
 	<inceptionYear>2014</inceptionYear>
@@ -45,8 +46,8 @@
 				<artifactId>maven-compiler-plugin</artifactId>
 				<version>2.3.2</version>
 				<configuration>
-					<source>1.7</source>
-					<target>1.7</target>
+					<source>${java.version}</source>
+					<target>${java.version}</target>
 				</configuration>
 			</plugin>
 			<plugin>
@@ -168,4 +169,4 @@
 			<scope>test</scope>
 		</dependency>
 	</dependencies>
-</project>
+</project>
\ No newline at end of file
diff --git a/src/main/java/org/beyene/sius/cache/Caches.java b/src/main/java/org/beyene/sius/cache/Caches.java
index fd48868..9200e9c 100644
--- a/src/main/java/org/beyene/sius/cache/Caches.java
+++ b/src/main/java/org/beyene/sius/cache/Caches.java
@@ -25,7 +25,7 @@
 
 public final class Caches {
 
-	private static Map<String, Provider> providers = new ConcurrentHashMap<>();
+	private static Map<String, Provider> providers = new ConcurrentHashMap<String, Provider>();
 	private static String DEFAULT_PROVIDER_NAME = "<def>";
 
 	static {
diff --git a/src/main/java/org/beyene/sius/cache/SimpleProvider.java b/src/main/java/org/beyene/sius/cache/SimpleProvider.java
index 858c417..f36fe82 100644
--- a/src/main/java/org/beyene/sius/cache/SimpleProvider.java
+++ b/src/main/java/org/beyene/sius/cache/SimpleProvider.java
@@ -25,6 +25,6 @@ final class SimpleProvider implements Provider {
 	@Override
 	public <D extends Dimension<D>, B extends Unit<D, B, B>, U extends Unit<D, B, U>> Cache<D, B, U> newInstance(
 			UnitId<D, B, U> id, int capacity) {
-		return new SimpleCache<>(capacity);
+		return new SimpleCache<D, B, U>(capacity);
 	}
 }
\ No newline at end of file
diff --git a/src/main/java/org/beyene/sius/example/Example.java b/src/main/java/org/beyene/sius/example/Example.java
index 38a7dd7..aecd4b2 100644
--- a/src/main/java/org/beyene/sius/example/Example.java
+++ b/src/main/java/org/beyene/sius/example/Example.java
@@ -17,6 +17,7 @@
 package org.beyene.sius.example;
 
 import java.util.Arrays;
+import java.util.List;
 
 import org.beyene.sius.dimension.Length;
 import org.beyene.sius.dimension.Mass;
@@ -82,7 +83,9 @@ public static void main(String[] args) {
 		Inch inch = Operation.convert(foot, UnitIdentifier.INCH);
 		System.out.println(String.format("Converted %s to %s", foot, inch));
 		
-		System.out.println(String.format("Summands \t= %s", Arrays.<Unit<Length, Meter, ?>>asList(FactoryLength.meter(1000), FactoryLength.mile(1), FactoryLength.meter(1000)).toString()));
+		@SuppressWarnings("unchecked")
+		List<Unit<Length, Meter, ?>> lengths = Arrays.<Unit<Length, Meter, ?>>asList(FactoryLength.meter(1000), FactoryLength.mile(1), FactoryLength.meter(1000));
+		System.out.println(String.format("Summands \t= %s", lengths.toString()));
 		System.out.println("Sum \t\t= " + Operation.add(FactoryLength.meter(1000), FactoryLength.mile(1), FactoryLength.meter(1000)));
 		
 		Adder<Length, Meter, Meter> adder = FunctorFactory.sum(UnitIdentifier.METER)
@@ -101,21 +104,6 @@ public static void main(String[] args) {
 		System.out.println(adder);
 		System.out.println(adder.apply());
 		
-		Meter sameRes = Operation.add(UnitIdentifier.METER,
-				lengthSecond,
-				lengthSecond,
-				lengthSecond,
-				lengthSecond,
-				lengthSecond,
-				lengthSecond,
-				lengthSecond,
-				lengthSecond,
-				lengthSecond,
-				lengthSecond,
-				foot,
-				foot);
-		System.out.println(sameRes);
-		
 		ArithmeticMean<Mass, KiloGram, KiloGram> mean = FunctorFactory.mean(UnitIdentifier.KILOGRAM)
 				.op(FactoryMass.kg(10))
 				.op(FactoryMass.kg(100))
diff --git a/src/main/java/org/beyene/sius/operation/Operation.java b/src/main/java/org/beyene/sius/operation/Operation.java
index 36449bb..b9c8431 100644
--- a/src/main/java/org/beyene/sius/operation/Operation.java
+++ b/src/main/java/org/beyene/sius/operation/Operation.java
@@ -19,8 +19,6 @@
 import org.beyene.sius.dimension.Dimension;
 import org.beyene.sius.dimension.composition.util.Fraction;
 import org.beyene.sius.dimension.composition.util.Product;
-import org.beyene.sius.operation.functor.Adder;
-import org.beyene.sius.operation.functor.FunctorFactory;
 import org.beyene.sius.unit.Unit;
 import org.beyene.sius.unit.UnitFactory;
 import org.beyene.sius.unit.UnitId;
@@ -98,30 +96,6 @@ public static <D extends Dimension<D>, B extends Unit<D, B, B>, OP1 extends Unit
 				+ Converter.convert(op2, op1.getIdentifier()).getValue());
 	}
 
-	/**
-	 * Adds (different) units of the same dimension.
-	 * 
-	 * @param targetId
-	 *            resulting unit
-	 * @param op
-	 *            first operand
-	 * @param ops
-	 *            further operands
-	 * @return sum
-	 * 
-	 * @param <D> dimension
-	 * @param <B> base unit of dimension
-	 * @param <OP> first operands unit
-	 * @param <TARGET_UNIT> target unit
-	 */
-	@SafeVarargs
-	public static <D extends Dimension<D>, B extends Unit<D, B, B>, OP extends Unit<D, B, OP>, TARGET_UNIT extends Unit<D, B, TARGET_UNIT>> TARGET_UNIT add(
-			UnitId<D, B, TARGET_UNIT> targetId, OP op, Unit<D, B, ?>... ops) {
-		Adder<D, B, TARGET_UNIT> adder = FunctorFactory.sum(targetId).op(op);
-		for (Unit<D, B, ?> o : ops)
-			adder.op(o);
-		return adder.apply();
-	}
 
 	/**
 	 * Subtracts two (different) units of the same dimension. Result is of same
diff --git a/src/main/java/org/beyene/sius/operation/functor/AbstractFunctor.java b/src/main/java/org/beyene/sius/operation/functor/AbstractFunctor.java
index ee1144c..a8d4083 100644
--- a/src/main/java/org/beyene/sius/operation/functor/AbstractFunctor.java
+++ b/src/main/java/org/beyene/sius/operation/functor/AbstractFunctor.java
@@ -28,7 +28,7 @@ abstract class AbstractFunctor<D extends Dimension<D>, B extends Unit<D, B, B>,
 	private final String functionName;
 	protected final UnitId<D, B, TARGET_UNIT> targetId;
 	
-	protected final List<Unit<D, B, ?>> operands = new LinkedList<>();
+	protected final List<Unit<D, B, ?>> operands = new LinkedList<Unit<D, B, ?>>();
 	protected TARGET_UNIT cachedResult;
 	
 	public AbstractFunctor(UnitId<D, B, TARGET_UNIT> targetId, String functionName) {
diff --git a/src/main/java/org/beyene/sius/unit/UnitFactory.java b/src/main/java/org/beyene/sius/unit/UnitFactory.java
index 3def7db..632e5af 100644
--- a/src/main/java/org/beyene/sius/unit/UnitFactory.java
+++ b/src/main/java/org/beyene/sius/unit/UnitFactory.java
@@ -29,7 +29,7 @@
 
 public final class UnitFactory {
 
-	private static final Map<UnitId<?, ?, ?>, Unit<?, ?, ?>> instanceMapMutable = new HashMap<>();
+	private static final Map<UnitId<?, ?, ?>, Unit<?, ?, ?>> instanceMapMutable = new HashMap<UnitId<?, ?, ?>, Unit<?, ?, ?>>();
 
 	/* initialize map */
 	static {
diff --git a/src/main/java/org/beyene/sius/unit/impl/CelsiusImpl.java b/src/main/java/org/beyene/sius/unit/impl/CelsiusImpl.java
index 81e5866..78b1498 100644
--- a/src/main/java/org/beyene/sius/unit/impl/CelsiusImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/CelsiusImpl.java
@@ -39,7 +39,7 @@ final class CelsiusImpl extends AbstractUnit<Temperature, Kelvin, Celsius> imple
 
 		int sizeStatic = Preferences.getInt("celsius.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("celsius.cache.static.low", 0), sizeStatic, CelsiusImpl.class);
+			staticCache = new StaticCache<Temperature, Kelvin, Celsius>(Preferences.getInt("celsius.cache.static.low", 0), sizeStatic, CelsiusImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/FahrenheitImpl.java b/src/main/java/org/beyene/sius/unit/impl/FahrenheitImpl.java
index 819b0a4..be69a0a 100644
--- a/src/main/java/org/beyene/sius/unit/impl/FahrenheitImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/FahrenheitImpl.java
@@ -39,7 +39,7 @@ final class FahrenheitImpl extends AbstractUnit<Temperature, Kelvin, Fahrenheit>
 
 		int sizeStatic = Preferences.getInt("fahrenheit.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("fahrenheit.cache.static.low", 0), sizeStatic, FahrenheitImpl.class);
+			staticCache = new StaticCache<Temperature, Kelvin, Fahrenheit>(Preferences.getInt("fahrenheit.cache.static.low", 0), sizeStatic, FahrenheitImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/FootImpl.java b/src/main/java/org/beyene/sius/unit/impl/FootImpl.java
index 934f005..01d6e93 100644
--- a/src/main/java/org/beyene/sius/unit/impl/FootImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/FootImpl.java
@@ -39,7 +39,7 @@ final class FootImpl extends AbstractUnit<Length, Meter, Foot> implements Foot {
 
 		int sizeStatic = Preferences.getInt("foot.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("foot.cache.static.low", 0), sizeStatic, FootImpl.class);
+			staticCache = new StaticCache<Length, Meter, Foot>(Preferences.getInt("foot.cache.static.low", 0), sizeStatic, FootImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/HourImpl.java b/src/main/java/org/beyene/sius/unit/impl/HourImpl.java
index 29977be..71ff9e8 100644
--- a/src/main/java/org/beyene/sius/unit/impl/HourImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/HourImpl.java
@@ -39,7 +39,7 @@ final class HourImpl extends AbstractUnit<Time, Second, Hour> implements Hour {
 
 		int sizeStatic = Preferences.getInt("hour.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("hour.cache.static.low", 0), sizeStatic, HourImpl.class);
+			staticCache = new StaticCache<Time, Second, Hour>(Preferences.getInt("hour.cache.static.low", 0), sizeStatic, HourImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/InchImpl.java b/src/main/java/org/beyene/sius/unit/impl/InchImpl.java
index cfb9e87..8b1a5a6 100644
--- a/src/main/java/org/beyene/sius/unit/impl/InchImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/InchImpl.java
@@ -39,7 +39,7 @@ final class InchImpl extends AbstractUnit<Length, Meter, Inch> implements Inch {
 
 		int sizeStatic = Preferences.getInt("inch.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("inch.cache.static.low", 0), sizeStatic, InchImpl.class);
+			staticCache = new StaticCache<Length, Meter, Inch>(Preferences.getInt("inch.cache.static.low", 0), sizeStatic, InchImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/KelvinImpl.java b/src/main/java/org/beyene/sius/unit/impl/KelvinImpl.java
index bc4152b..9c1a880 100644
--- a/src/main/java/org/beyene/sius/unit/impl/KelvinImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/KelvinImpl.java
@@ -37,7 +37,7 @@ final class KelvinImpl extends AbstractUnit<Temperature, Kelvin, Kelvin> impleme
 
 		int sizeStatic = Preferences.getInt("kelvin.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("kelvin.cache.static.low", 0), sizeStatic, KelvinImpl.class);
+			staticCache = new StaticCache<Temperature, Kelvin, Kelvin>(Preferences.getInt("kelvin.cache.static.low", 0), sizeStatic, KelvinImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/KiloGramImpl.java b/src/main/java/org/beyene/sius/unit/impl/KiloGramImpl.java
index eefd9f8..82c104b 100644
--- a/src/main/java/org/beyene/sius/unit/impl/KiloGramImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/KiloGramImpl.java
@@ -37,7 +37,7 @@ final class KiloGramImpl extends AbstractUnit<Mass, KiloGram, KiloGram> implemen
 
 		int sizeStatic = Preferences.getInt("kg.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("kg.cache.static.low", 0), sizeStatic, KiloGramImpl.class);
+			staticCache = new StaticCache<Mass, KiloGram, KiloGram>(Preferences.getInt("kg.cache.static.low", 0), sizeStatic, KiloGramImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/MeterImpl.java b/src/main/java/org/beyene/sius/unit/impl/MeterImpl.java
index 56a7dca..5c0e1ca 100644
--- a/src/main/java/org/beyene/sius/unit/impl/MeterImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/MeterImpl.java
@@ -38,7 +38,7 @@ final class MeterImpl extends AbstractUnit<Length, Meter, Meter> implements Mete
 
 		int sizeStatic = Preferences.getInt("meter.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("meter.cache.static.low", 0), sizeStatic, MeterImpl.class);
+			staticCache = new StaticCache<Length, Meter, Meter>(Preferences.getInt("meter.cache.static.low", 0), sizeStatic, MeterImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/MeterPerSecondImpl.java b/src/main/java/org/beyene/sius/unit/impl/MeterPerSecondImpl.java
index 785026b..742fc5f 100644
--- a/src/main/java/org/beyene/sius/unit/impl/MeterPerSecondImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/MeterPerSecondImpl.java
@@ -42,7 +42,7 @@ final class MeterPerSecondImpl extends AbstractUnit<Speed, MeterPerSecond, Meter
 
 		int sizeStatic = Preferences.getInt("mps.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("mps.cache.static.low", 0), sizeStatic, MeterPerSecondImpl.class);
+			staticCache = new StaticCache<Speed, MeterPerSecond, MeterPerSecond>(Preferences.getInt("mps.cache.static.low", 0), sizeStatic, MeterPerSecondImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/MileImpl.java b/src/main/java/org/beyene/sius/unit/impl/MileImpl.java
index 4eebe2b..f9e4e55 100644
--- a/src/main/java/org/beyene/sius/unit/impl/MileImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/MileImpl.java
@@ -39,7 +39,7 @@ final class MileImpl extends AbstractUnit<Length, Meter, Mile> implements Mile {
 
 		int sizeStatic = Preferences.getInt("mile.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("mile.cache.static.low", 0), sizeStatic, MileImpl.class);
+			staticCache = new StaticCache<Length, Meter, Mile>(Preferences.getInt("mile.cache.static.low", 0), sizeStatic, MileImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/MilesPerHourImpl.java b/src/main/java/org/beyene/sius/unit/impl/MilesPerHourImpl.java
index d002a50..abcf9a0 100644
--- a/src/main/java/org/beyene/sius/unit/impl/MilesPerHourImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/MilesPerHourImpl.java
@@ -46,7 +46,7 @@ final class MilesPerHourImpl extends AbstractUnit<Speed, MeterPerSecond, MilesPe
 
 		int sizeStatic = Preferences.getInt("mph.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("mph.cache.static.low", 0), sizeStatic, MilesPerHourImpl.class);
+			staticCache = new StaticCache<Speed, MeterPerSecond, MilesPerHour>(Preferences.getInt("mph.cache.static.low", 0), sizeStatic, MilesPerHourImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/MinuteImpl.java b/src/main/java/org/beyene/sius/unit/impl/MinuteImpl.java
index 65b3203..e08c390 100644
--- a/src/main/java/org/beyene/sius/unit/impl/MinuteImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/MinuteImpl.java
@@ -39,7 +39,7 @@ final class MinuteImpl extends AbstractUnit<Time, Second, Minute> implements Min
 
 		int sizeStatic = Preferences.getInt("minute.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("minute.cache.static.low", 0), sizeStatic, MinuteImpl.class);
+			staticCache = new StaticCache<Time, Second, Minute>(Preferences.getInt("minute.cache.static.low", 0), sizeStatic, MinuteImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/PoundImpl.java b/src/main/java/org/beyene/sius/unit/impl/PoundImpl.java
index 94b22b8..0578e96 100644
--- a/src/main/java/org/beyene/sius/unit/impl/PoundImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/PoundImpl.java
@@ -39,7 +39,7 @@ final class PoundImpl extends AbstractUnit<Mass, KiloGram, Pound> implements Pou
 
 		int sizeStatic = Preferences.getInt("pound.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("pound.cache.static.low", 0), sizeStatic, PoundImpl.class);
+			staticCache = new StaticCache<Mass, KiloGram, Pound>(Preferences.getInt("pound.cache.static.low", 0), sizeStatic, PoundImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/SecondImpl.java b/src/main/java/org/beyene/sius/unit/impl/SecondImpl.java
index d23a586..e3d4bab 100644
--- a/src/main/java/org/beyene/sius/unit/impl/SecondImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/SecondImpl.java
@@ -37,7 +37,7 @@ final class SecondImpl extends AbstractUnit<Time, Second, Second> implements Sec
 
 		int sizeStatic = Preferences.getInt("second.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("second.cache.static.low", 0), sizeStatic, SecondImpl.class);
+			staticCache = new StaticCache<Time, Second, Second>(Preferences.getInt("second.cache.static.low", 0), sizeStatic, SecondImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/StaticCache.java b/src/main/java/org/beyene/sius/unit/impl/StaticCache.java
index e1b3741..8285f99 100644
--- a/src/main/java/org/beyene/sius/unit/impl/StaticCache.java
+++ b/src/main/java/org/beyene/sius/unit/impl/StaticCache.java
@@ -43,10 +43,17 @@ public StaticCache(
 		for (int k = 0; k < cache.length; k++)
 			try {
 				cache[k] = (SELF) implementingClass.getDeclaredConstructor(double.class).newInstance(j++);
-			} catch (InstantiationException | IllegalAccessException
-					| IllegalArgumentException | InvocationTargetException
-					| NoSuchMethodException | SecurityException e) {
-				// not supposed to happen
+			} catch (InstantiationException e) {
+				throw new IllegalStateException(e);
+			} catch (IllegalAccessException e) {
+				throw new IllegalStateException(e);
+			} catch (IllegalArgumentException e) {
+				throw new IllegalStateException(e);
+			} catch (InvocationTargetException e) {
+				throw new IllegalStateException(e);
+			} catch (NoSuchMethodException e) {
+				throw new IllegalStateException(e);
+			} catch (SecurityException e) {
 				throw new IllegalStateException(e);
 			}
 	}
diff --git a/src/main/java/org/beyene/sius/unit/impl/YardImpl.java b/src/main/java/org/beyene/sius/unit/impl/YardImpl.java
index 4f0d34a..b496512 100644
--- a/src/main/java/org/beyene/sius/unit/impl/YardImpl.java
+++ b/src/main/java/org/beyene/sius/unit/impl/YardImpl.java
@@ -39,7 +39,7 @@ final class YardImpl extends AbstractUnit<Length, Meter, Yard> implements Yard {
 
 		int sizeStatic = Preferences.getInt("yard.cache.static.size", 1);
 		if (sizeStatic > 0)
-			staticCache = new StaticCache<>(Preferences.getInt("yard.cache.static.low", 0), sizeStatic, YardImpl.class);
+			staticCache = new StaticCache<Length, Meter, Yard>(Preferences.getInt("yard.cache.static.low", 0), sizeStatic, YardImpl.class);
 		else
 			staticCache = null;
 	}
diff --git a/src/test/java/org/beyene/sius/cache/SimpleCacheTest.java b/src/test/java/org/beyene/sius/cache/SimpleCacheTest.java
index d805331..7fe5354 100644
--- a/src/test/java/org/beyene/sius/cache/SimpleCacheTest.java
+++ b/src/test/java/org/beyene/sius/cache/SimpleCacheTest.java
@@ -28,7 +28,7 @@ public class SimpleCacheTest {
 
 	@Test
 	public void testLookUp() throws Exception {
-		SimpleCache<Time, Second, Hour> cache = new SimpleCache<>(5);
+		SimpleCache<Time, Second, Hour> cache = new SimpleCache<Time, Second, Hour>(5);
 
 		double value = 5;
 		Hour h = FactoryTime.hour(value);
@@ -41,7 +41,7 @@ public void testLookUp() throws Exception {
 	@Test
 	public void testPut() throws Exception {
 		int size = 10;
-		SimpleCache<Time, Second, Minute> cache = new SimpleCache<>(size);
+		SimpleCache<Time, Second, Minute> cache = new SimpleCache<Time, Second, Minute>(size);
 
 		int min = 1000;
 		boolean flag = true;
diff --git a/src/test/java/org/beyene/sius/unit/impl/AbstractUnitTest.java b/src/test/java/org/beyene/sius/unit/impl/AbstractUnitTest.java
index 5b59b93..1b71468 100644
--- a/src/test/java/org/beyene/sius/unit/impl/AbstractUnitTest.java
+++ b/src/test/java/org/beyene/sius/unit/impl/AbstractUnitTest.java
@@ -42,7 +42,7 @@ public class AbstractUnitTest {
 	@Before
 	public void setUp() {
 		dynamicCache = Caches.newInstance(unitId, 10);
-		staticCache = new StaticCache<>(0, 10, MeterImpl.class);
+		staticCache = new StaticCache<Length, Meter, Meter>(0, 10, MeterImpl.class);
 		m = new MeterImpl(value, dimension, unitId, interfaceClass, dynamicCache, staticCache);
 	}
 	
@@ -94,6 +94,16 @@ public void testValueOf() throws Exception {
 		Meter dynCache1 =  m.valueOf(oneThird);
 		Meter dynCache2 =  m.valueOf(oneThird);
 		Assert.assertTrue(dynCache1 == dynCache2);
+		
+		m = new MeterImpl(oneThird, dimension, unitId, interfaceClass, null, null);
+		Meter sameInstance = m.valueOf(oneThird);
+		Assert.assertTrue(m == sameInstance);
+		
+		double twoThird = 2d /  3d;
+		Meter m2 = m.valueOf(twoThird);
+		Meter notSame = m.valueOf(twoThird);
+		Assert.assertTrue(m2 != notSame);
+		
 	}
 
 	@Test
diff --git a/src/test/java/org/beyene/sius/unit/impl/StaticCacheTest.java b/src/test/java/org/beyene/sius/unit/impl/StaticCacheTest.java
index b54c4bb..9341d5a 100644
--- a/src/test/java/org/beyene/sius/unit/impl/StaticCacheTest.java
+++ b/src/test/java/org/beyene/sius/unit/impl/StaticCacheTest.java
@@ -28,7 +28,7 @@ public class StaticCacheTest {
 	public void testCtor1() throws Exception {
 		int low = -5;
 		int size = 10;
-		StaticCache<Length, Meter, Inch> staticCache = new StaticCache<>(low,
+		StaticCache<Length, Meter, Inch> staticCache = new StaticCache<Length, Meter, Inch>(low,
 				size, InchImpl.class);
 
 		int start = low;
@@ -40,7 +40,7 @@ public void testCtor1() throws Exception {
 	@Test(expected = IllegalStateException.class)
 	public void testCtor2() throws Exception {
 		@SuppressWarnings("unused")
-		StaticCache<Length, Meter, Inch> staticCache = new StaticCache<>(0, 5, Inch.class);
+		StaticCache<Length, Meter, Inch> staticCache = new StaticCache<Length, Meter, Inch>(0, 5, Inch.class);
 		Assert.fail("Class parameter has to be class of an interface to throw the expected exception!");
 	}
 }
\ No newline at end of file