How to call private method from another class in java

You can call the private method from outside the class by changing the runtime behaviour of the class.

With the help of java.lang.Class class and java.lang.reflect.Method class, we can call a private method from any other class.

Required methods of Method class

1) public void setAccessible(boolean status) throws SecurityException sets the accessibility of the method.

2) public Object invoke(Object method, Object... args) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException is used to invoke the method.

Required method of Class class

1) public Method getDeclaredMethod(String name,Class[] parameterTypes)throws NoSuchMethodException,SecurityException: returns a Method object that reflects the specified declared method of the class or interface represented by this Class object.

Example of calling private method from another class

Let's see the simple example to call private method from another class.

File: A.java

File: MethodCall.java

Output:

hello java

Another example to call parameterized private method from another class

Let's see the example to call parameterized private method from another class

File: A.java

File: M.java

Output:

64

Accessing Private Constructors of a class

We know that constructors of a class are a special kind of method this is used to instantiate the class. To access the private constructor, we use the method getDeclaredConstructor(). The getDeclaredConstructor() is used to access a parameterless as well as a parametrized constructor of a class. The following example shows the same.

FileName: PvtConstructorDemo.java

Output:

Vehicle Id: 20
Vehicle Name: Indica
 -------------------------- 
Vehicle Id: 30
Vehicle Name: Alto