With Java newInstacnce() of class Class, we can create an object as you will do with new keyword.
Example on Java newInstance
public class Student
{
int marks;
public void display()
{
System.out.println("Hello 1");
}
public static void main(String args[]) throws InstantiationException, IllegalAccessException, ClassNotFoundException
{
Student std1 = new Student();
std1.marks = 50;
Class cls1 = std1.getClass();
Object obj1 = cls1.newInstance(); // Observe, usage of Java newInstance
Student std2 = (Student) obj1;
System.out.println("\nstd1 marks: " + std1.marks); // prints 50
System.out.println("std2 marks: " + std2.marks); // prints 0
std2.display(); // Hello 1
// the other way of getting Class object
Class cls2 = Class.forName("Student");
Object obj2 = cls2.newInstance();
Student std3 = (Student) obj2;
std3.display(); // Hello 1
}
}
Output screenshot on Java newInstance Example
The newInstance() method of java.lang.Class returns an object of class Object represented by a Class object. It is very confusing. Let us see what I mean.
Student std1 = new Student();
Class cls1 = std1.getClass();
Object obj1 = cls1.newInstance();
Student std2 = (Student) obj1;
The getClass() method of Object class returns an object of Class, cls1. Here, the Class object cls1 represents a Student class object. The newInstance() method of java.lang.Class returns an object Object class, obj1. The obj1 represents an object of Student. If required, we can cast this obj1 to Student class object, as I did in the above code. These objects can be used to call the methods of Student.
System.out.println(“\nstd1 marks: ” + std1.marks); // prints 50
System.out.println(“std2 marks: ” + std2.marks); // prints 0
The Student objects std1 and std2 are very different. They maintain encapsulation. For this reason, std2.marks prints 0 (the default value of marks) and not 50 of std1 marks.
The newInstance() method throws two checked exceptions – InstantiationException and IllegalAccessException.
Class cls2 = Class.forName(“Student”);
Object obj2 = cls2.newInstance();
There is another way of getting Class object. It is by using forName() method of Class as in the above code.
The forName() method throws ClassNotFoundException.
Let us see what we can do more with Class object.
Java newInstance
With the Class object, following operations can be performed. There are three methods in the Class.
1. public native boolean isInterface();
2. public native boolean isArray();
3. public native boolean isPrimitive();
The above methods are used in the following program.
interface Test { }
public class Student
{
public static void main(String args[]) throws InstantiationException, IllegalAccessException, ClassNotFoundException
{
Student std1 = new Student();
Class cls1 = std1.getClass();
System.out.println("\nStudent class name: " + cls1.getName());
System.out.println("Student is interface: " + cls1.isInterface());
System.out.println("Student is array: " + cls1.isArray());
int marks[] = {50, 60, 70 };
Class cls2 = marks.getClass();
System.out.println("\nmarks is array: " + cls2.isArray());
Class cls3 = Class.forName("Test");
System.out.println("\nTest is interface: " + cls3.isInterface());
}
}
With the methods isInterface() and isArray(), we can check a class object represents an interface or an Array.