Programming Tutorials

java.lang.reflect package

By: Riktesh Srivastava in Java Tutorials on 2023-03-25  

In this tutorial, I will explain the aspects of java.lang.reflect package. This package returns, constructors, fields, and methods of the given package. Each and every program begins by using the forName() method of Class to get a class object for java.lang.Object. Once this is obtained, getConstructors(), getFields(), and getMethods() are used to analyze this class object. They return arrays of Constructor, Field, and Method objects that provide the information about the object. The Constructor, Field, and Method classes define several methods that can be used to obtain information about an object.

Consider the example given below:

import java.lang.reflect.*;

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

        try {
            Class<Object> c = Object.class;
            System.out.println("Constructors:");
            Constructor[] constructors = c.getConstructors();

            for (int i = 0; i < constructors.length; i++) {
                System.out.println(" " + constructors[i]);
            }
            System.out.println("Fields:");
            Field fields[] = c.getFields();
            for (int i = 0; i < fields.length; i++) {
                System.out.println(" " + fields[i]);
            }
            System.out.println("Methods:");
            Method methods[] = c.getMethods();

            for (int i = 0; i < methods.length; i++) {
                System.out.println(" " + methods[i]);
            }
        } catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

The given program demonstrates the use of Java reflection to get information about the class "java.lang.Object". Here's how it works:

• The program first calls the Class.forName() method to get a reference to the java.lang.Object class.
• The getConstructors() method is then called on the Class object to retrieve an array of Constructor objects that represent the public constructors of the class.
• A for loop is used to iterate over the Constructor array and print each constructor to the console.
• Similarly, the getFields() method is called on the Class object to retrieve an array of Field objects that represent the public fields of the class. Another for loop is used to print each field to the console.
• Finally, the getMethods() method is called on the Class object to retrieve an array of Method objects that represent the public methods of the class. Another for loop is used to print each method to the console.

Here's an example output of the program:

Constructors:
 public java.lang.Object()
Fields:
 public static final java.lang.Class java.lang.Object.CLASS
Methods:
 public boolean java.lang.Object.equals(java.lang.Object)
 public java.lang.String java.lang.Object.toString()
 public native int java.lang.Object.hashCode()
 public final native java.lang.Class java.lang.Object.getClass()
 public final native void java.lang.Object.notify()
 public final native void java.lang.Object.notifyAll()
 public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
 public final void java.lang.Object.wait() throws java.lang.InterruptedException
 public final void java.lang.Object.wait(long) throws java.lang.InterruptedException