diff --git a/jdk/java/lang/Double.js b/jdk/java/lang/Double.js
index c4924f8..fac3e6d 100755
--- a/jdk/java/lang/Double.js
+++ b/jdk/java/lang/Double.js
@@ -10,6 +10,13 @@ jdk.imports['java.lang.Double'].load = async () => {
 	Double.compare = (a, b) => {
 		return a - b;
 	};
+	Double.valueOf = (a) => {
+		let val = Number(a);
+		if (isNaN(val)) {
+			throw new Error('NumberFormatException: For input string: ' + a);
+		}
+		return val;
+	};
 	Double.MAX_VALUE = Number.MAX_VALUE;
 	Double.POSITIVE_INFINITY = Number.POSITIVE_INFINITY;
 	Double.NEGATIVE_INFINITY = Number.NEGATIVE_INFINITY;
diff --git a/jdk/java/lang/Float.js b/jdk/java/lang/Float.js
index dd9a071..ceadcd7 100755
--- a/jdk/java/lang/Float.js
+++ b/jdk/java/lang/Float.js
@@ -6,6 +6,13 @@ jdk.imports['java.lang.Float'].load = async () => {
 	Float.compare = (a, b) => {
 		return a - b;
 	};
+	Float.valueOf = (a) => {
+		let val = Number(a);
+		if (isNaN(val)) {
+			throw new Error('NumberFormatException: For input string: ' + a);
+		}
+		return val;
+	};
 	Float.MAX_VALUE = Number.MAX_VALUE;
 	Float.POSITIVE_INFINITY = Number.POSITIVE_INFINITY;
 	Float.NEGATIVE_INFINITY = Number.NEGATIVE_INFINITY;
diff --git a/jdk/java/lang/Integer.js b/jdk/java/lang/Integer.js
index 02a6253..b513389 100755
--- a/jdk/java/lang/Integer.js
+++ b/jdk/java/lang/Integer.js
@@ -6,6 +6,13 @@ jdk.imports['java.lang.Integer'].load = async () => {
 	Integer.compare = (a, b) => {
 		return a - b;
 	};
+	Integer.valueOf = (a) => {
+		let val = Number(a);
+		if (isNaN(val)) {
+			throw new Error('NumberFormatException: For input string: ' + a);
+		}
+		return val;
+	};
 	Integer.MAX_VALUE = Number.MAX_VALUE;
 	Integer.POSITIVE_INFINITY = Number.POSITIVE_INFINITY;
 	Integer.NEGATIVE_INFINITY = Number.NEGATIVE_INFINITY;
diff --git a/jdk/java/lang/Long.js b/jdk/java/lang/Long.js
index 90f05ed..507a3b6 100755
--- a/jdk/java/lang/Long.js
+++ b/jdk/java/lang/Long.js
@@ -6,6 +6,13 @@ jdk.imports['java.lang.Long'].load = async () => {
 	Long.compare = (a, b) => {
 		return a - b;
 	};
+	Long.valueOf = (a) => {
+		let val = Number(a);
+		if (isNaN(val)) {
+			throw new Error('NumberFormatException: For input string: ' + a);
+		}
+		return val;
+	};
 	Long.MAX_VALUE = Number.MAX_VALUE;
 	Long.POSITIVE_INFINITY = Number.POSITIVE_INFINITY;
 	Long.NEGATIVE_INFINITY = Number.NEGATIVE_INFINITY;
diff --git a/jdk/java/lang/Short.js b/jdk/java/lang/Short.js
index d28792a..2c0e204 100755
--- a/jdk/java/lang/Short.js
+++ b/jdk/java/lang/Short.js
@@ -6,6 +6,13 @@ jdk.imports['java.lang.Short'].load = async () => {
 	Short.compare = (a, b) => {
 		return a - b;
 	};
+	Short.valueOf = (a) => {
+		let val = Number(a);
+		if (isNaN(val)) {
+			throw new Error('NumberFormatException: For input string: ' + a);
+		}
+		return val;
+	};
 	Short.MAX_VALUE = Number.MAX_VALUE;
 	Short.POSITIVE_INFINITY = Number.POSITIVE_INFINITY;
 	Short.NEGATIVE_INFINITY = Number.NEGATIVE_INFINITY;
diff --git a/jdk/java/lang/String.js b/jdk/java/lang/String.js
index d962470..8c83caf 100755
--- a/jdk/java/lang/String.js
+++ b/jdk/java/lang/String.js
@@ -34,4 +34,12 @@ jdk.imports['java.lang.String'].load = async () => {
 		return new Formatter().format(format, ...args);
 	};
 	jdk.java.lang.String = String;
+
+	Number.prototype.toUpperCase = function () {
+		return this + '';
+	};
+
+	Number.prototype.toLowerCase = function () {
+		return this + '';
+	};
 };
diff --git a/package.json b/package.json
index 72d6ebe..5ebf36e 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
 	"name": "java2js",
-	"version": "1.2.18",
+	"version": "1.2.19",
 	"description": "Converts Java to JavaScript and runs it with a JS JDK",
 	"main": "jdk.js",
 	"scripts": {