ClassLoader getDefinedPackage(String) in Java

getDefinedPackage(String): This method is available in the java.lang.ClassLoader class of Java.

Syntax:

Package java.lang.ClassLoader.getDefinedPackage(String name)

This method takes one argument. This method returns a Package of the given name that has been defined by this class loader.

Parameters: One parameter is required for this method.

name: The package name.

Returns: The Package of the given name that has been defined by this class loader, or null if not found.

Throws:

1. NullPointerException - if the name is null.

Approach 1: When no exception

Java

package com.ClassLoader;

public class ClassLoadergetDefinedPackage {
    public static void main(String[] args) {

        ClassLoader classLoader = 
                           ClassLoader.getSystemClassLoader();

        String name = "java.lang.String";

        System.out.println(classLoader.getDefinedPackage(name));
    }
}

Output:

null

Approach 2: NullPointerException

Java

package com.ClassLoader;

public class ClassLoadergetDefinedPackage {
    public static void main(String[] args) {

        ClassLoader classLoader =
                         ClassLoader.getSystemClassLoader();

        String name = null;

        System.out.println(classLoader.getDefinedPackage(name));
    }
}

Output:

Exception in thread "main" java.lang.NullPointerException: name cannot be null
	at java.base/java.util.Objects.requireNonNull(Objects.java:233)
	at java.base/java.lang.ClassLoader.getDefinedPackage(ClassLoader.java:2247)
	at com.ClassLoader.ClassLoadergetDefinedPackage.main(ClassLoadergetDefinedPackage.java:10)

Some other methods of ClassLoader class

clearAssertionStatus(): This method sets the default assertion status for this class loader to false and discards any package defaults or class assertion status settings associated with the class loader.

getDefinedPackage(String): This method returns a Package of the given name that has been defined by this class loader.

getDefinedPackages(): This method returns all of the Packages that have been defined by this class loader. 

getName(): This method returns the name of this class loader or null if this class loader is not named.

getParent(): This method returns the parent class loader for delegation. Some implementations may use null to represent the bootstrap class loader.

ClassLoader.getPlatformClassLoader(): This method returns the platform class loader. All platform classes are visible to the platform class loader.

getResource(String): This method finds the resource with the given name.

getResourceAsStream(String): This method returns an input stream for reading the specified resource.

getResources(String): This method finds all the resources with the given name.

ClassLoader.getSystemClassLoader(): This method returns the system class loader. 

ClassLoader.getSystemResource(String): This method finds a resource of the specified name from the search path used to load classes. 

ClassLoader.getSystemResourceAsStream(String): This method is open for reading, a resource of the specified name from the search path used to load classes.

ClassLoader.getSystemResources(String): This method finds all resources of the specified name from the search path used to load classes.

getUnnamedModule(): This method returns the unnamed Module for this class loader.

isRegisteredAsParallelCapable(): This method returns true if this class loader is registered as parallel capable, otherwise false.

loadClass(String): This method loads the class with the specified binary name.

resources(String): This method returns a stream whose elements are the URLs of all the resources with the given name.

setClassAssertionStatus(String, boolean): This method sets the desired assertion status for the named top-level class in this class loader and any nested classes contained therein.

setDefaultAssertionStatus(boolean): This method sets the default assertion status for this class loader.

setPackageAssertionStatus(String, boolean): This method sets the package default assertion status for the named package.