Java Program to Print object of a class

Introduction

Java is widely used for its powerful object-oriented capabilities, including class definition, object creation, and method invocation. A common task in Java programming is to print an object's state, which can be achieved by overriding the toString() method in a class. This allows for a more readable and informative output when an object is printed, rather than displaying the default hash code representation.

In this article, you will learn how to effectively print object details in Java by creating classes and overriding the toString() method. You'll explore several examples that demonstrate how to customize the output to make debugging and logging more informative and useful.

Basic Printing of a Class Object

Override the toString() Method

1. Define a simple class with some attributes.

2. Override the toString() method to customize the output when an object of the class is printed.

   java Copy

   public class Person {
       private String name;
       private int age;
   
       public Person(String name, int age) {
           this.name = name;
           this.age = age;
       }
   
       @Override
       public String toString() {
           return "Person{name='" + name + "', age=" + age + '}';
       }
   }
   

   This example defines a Person class with properties name and age and overrides the toString() method to return a string that clearly displays the object's attributes.

Instantiate and Print the Object

1. Create an object of the Person class.

2. Print the object using System.out.println().

   java Copy

   public class Main {
       public static void main(String[] args) {
           Person person = new Person("John Doe", 30);
           System.out.println(person);
       }
   }
   

   When this code runs, it prints Person{name='John Doe', age=30}, thanks to the overridden toString() method.

Advanced Example with Complex Objects

Define a Class with Composite Attributes

1. Create a new class that includes various data types and possibly other objects as attributes.

2. Override toString() to provide a detailed representation of the object.

   java Copy

   public class Employee {
       private String name;
       private int id;
       private Department department;
   
       public Employee(String name, int id, Department department) {
           this.name = name;
           this.id = id;
           this.department = department;
       }
   
       @Override
       public String toString() {
           return "Employee{" +
                  "name='" + name + '\'' +
                  ", id=" + id +
                  ", department=" + department +
                  '}';
       }
   }
   
   public class Department {
       private String name;
   
       public Department(String name) {
           this.name = name;
       }
   
       @Override
       public String toString() {
           return "Department{name='" + name + "'}";
       }
   }
   

   This example includes an Employee class that has a Department object as an attribute. Both classes override the toString() method for meaningful printing.

Instantiate and Print Composite Object

1. Create objects of Employee and Department.

2. Print the Employee object to see detailed output including the Department information.

   java Copy

   public class Main {
       public static void main(String[] args) {
           Department department = new Department("IT");
           Employee employee = new Employee("Alice Johnson", 101, department);
           System.out.println(employee);
       }
   }
   

   Here, the output will display all the attributes of Employee, including the nested Department details: Employee{name='Alice Johnson', id=101, department=Department{name='IT'}}.

Conclusion

By overriding the toString() method in Java classes, you gain control over how objects are represented as strings, which is extremely useful for monitoring and debugging purposes. You have seen how this can be applied to simple objects and to more complex scenarios involving nested objects. Implement these techniques in your Java applications to enhance the readability and maintainability of logging and output statements, ensuring that object states are clear and informative when printed.