Important points on Java classpath

Important points on Java classpath

1. Classpath in Java is an environment variable used by Java Virtual machine to locate or find java classes during class loading.

2. You can override value of Classpath in Java defined by environment variable CLASSPATH by providing JVM command line option –cp or –classpath while running your application.

3. If two classes with same name exist in Java Classpath then the class which comes earlier in Classpath will be picked by Java Virtual Machine.

4. By default CLASSPATH in Java points to current directory denoted by "." and it will look for any class only in current directory.

5. When you use the -jar command line  option to run your program as an executable JAR, then the Java CLASSPATH environment variable will be ignored, and also the -cp and -classpath switches will be ignored and In this case you can set your java classpath in the META-INF/MANIFEST.MF file by using the Class-Path attribute.

6. In Unix / Linux Java Classpath contains names of directory with colon “:” separated , On Windows Java Classpath will be  semi colon “;” separated while if you defined java classpath in Manifest file those will be space separated.

7. You can check value of classpath in java inside your application by looking at following system property “java.class.path”

System.getProperty("java.class.path")

8. ClassNotFoundException is an Exception and will be thrown when Java program dynamically tries to load a particular Class at Runtime and don’t find that on Java classpath due to result of Class.forName() or loadClass() method invocation.

9. NoClassDefFoundError comes when a particular class was present in Java Classpath during compile time but not available during runtime on Classpath in Java.