In this tutorial, we will learn how to store user-defined (custom) class objects in Java ArrayList in an easy way and step by step.
In the previous ArrayList tutorial, we have learned that ArrayList class uses generic from Java 1.5 or later. Using generic, ArrayList class can be used to store any type of object.
In other words, we can store multiple types of objects in an ArrayList using generic feature.
For example, we could have an ArrayList of Book objects, an ArrayList of Employee objects, or an ArrayList of Strings. The specified type must be a class, not a primitive type.
If you want to store primitive data types in ArrayList, you will have to use one of java wrapper classes such as Integer, Double, or Character.
Declaration of ArrayList Objects
The syntax for declaring an ArrayList of objects is as follows:
ArrayList<ClassName> arrayListName;
Inside angle brackets, we declare the class types of objects that will be stored in ArrayList. Let’s understand with the help of some examples.
1. ArrayList<Employee> emp = new ArrayList<Employee>();
// Here, Employee is the name of class.
// ArrayList<Employee> indicates that only Employee objects can be stored in the array list.
2. ArrayList<Book> b = new ArrayList<Book>();How to store User-defined (Custom) Class Objects in Java ArrayList?
Let’s take an example program where we will store user-defined (custom) class objects in ArrayList.
Suppose there are three students whose name, id, rollNo have to add to the custom ArrayList. First, we will create a class Student.
In this class, we will define a constructor and three instance variables name, id, and rollNo of data type String, int, and int respectively. Look at the below program source code.
Program code 1:
package customArrayList;
public class Student
{
// Create instance variables name, id, and rollNo of data type String, int, and int respectively.
String name;
int id;
int rollNo;
// Create three parameters constructor with parameters name, id, and rollNo.
Student(String name, int id, int rollNo)
{
this.name = name;
this.rollNo = rollNo;
this.id = id;
}
}Now create another class addingData in which we will store three Student class objects in the ArrayList.
package customArrayList;
import java.util.ArrayList;
public class AddingData
{
// Create a ArrayList method of generic type 'Student'.
ArrayList<Student> studentData()
{
// Create three objects of the class Student and pass arguments to the constructor.
Student s1 = new Student("Deep", 1234, 04);
Student s2 = new Student("Shubh", 4321, 20 );
Student s3 = new Student("Riddhi", 1212, 02);
// Create the object of ArrayList of generic type 'Student'.
ArrayList<Student> studentlist = new ArrayList<Student>();
// Now add Student objects in the ArrayList using reference variable studentlist.
studentlist.add(s1);
studentlist.add(s2);
studentlist.add(s3);
// Return object reference variable 'studentlist' of the array list to the method 'studentValue'.
return studentlist;
}
}Now create one more class to retrieve students data from the above class’s studentData() method and iterate over them to get the student detail.
package customArrayList;
import java.util.ArrayList;
public class RetriveStudents
{
public static void main(String[] args)
{
// Call AddingData class by creating object of that class.
AddingData data = new AddingData();
// Call studentData() method using reference variable data.
ArrayList<Student> listst = data.studentData();
// Now iterate and display all the Student data.
for(Student st:listst)
{
System.out.println("Student's name: " +st.name);
System.out.println("Student ID " +st.id);
System.out.println("Roll number: " +st.rollNo);
}
}
}Output:
Student's name: Deep
Student ID 1234
Roll number: 4
Student's name: Shubh
Student ID 4321
Roll number: 20
Student's name: Riddhi
Student ID 1212
Roll number: 2The same program can also be done without using any constructor. Look at the below source code and follow all steps.
Program code 2:
package customArrayList2;
public class Student
{
// Declare instance variables name, phyMarks, mathsMarks, chemMarks, total, and per.
String name;
int phyMarks;
int mathsMarks;
int chemMarks;
int total;
float per;
}package customArrayList2;
import java.util.ArrayList;
public class Studentdata
{
// Declare an ArrayList method of generic type Student.
ArrayList<Student> addData()
{
// Create two objects s1 and s2 of the student class and initialize the value of variables using reference variable s1 and s2.
Student s1 = new Student();
s1.name = "Shubh";
s1.phyMarks = 95;
s1.mathsMarks = 100;
s1.chemMarks = 90;
s1.total = 95 + 100 + 90;
s1.per = ((s1.total)*100)/300;
Student s2 = new Student();
s2.name = "Deep";
s2.phyMarks = 80;
s2.mathsMarks = 85;
s2.chemMarks = 90;
s2.total = 80 + 85 + 90;
s2.per = ((s2.total)*100)/300;
// Create an ArrayList object of generic type Student.
ArrayList<Student> al = new ArrayList<Student>();
// Call add() method to store student class objects in the array list using reference variable al.
al.add(s1);
al.add(s2);
return al;
}
}package customArrayList2;
import java.util.ArrayList;
public class RetriveStudentData
{
// Declare an instance method.
void fetchStudentData()
{
// Create an object of the Studentdata class.
Studentdata stdata = new Studentdata();
// Call addData() method using reference variable stdata.
ArrayList<Student> listst = stdata.addData();
// Now iterate and display all the student data.
// enhance for loop - for each loop.
for(Student student:listst)
{
System.out.println("Name: " +student.name);
System.out.println("Physics Marks: " +student.phyMarks);
System.out.println("Maths Marks: " +student.mathsMarks);
System.out.println("Chemistry Marks: " +student.chemMarks);
System.out.println("Total Marks: " +student.total);
System.out.println("Percentage:" +student.per);
}
}
}In this example program, we will create a client class to test our logic.
package customArrayList2;
public class TestStudentOperation
{
public static void main(String[] args)
{
Studentdata st = new Studentdata();
st.addData();
RetriveStudentData rsd = new RetriveStudentData();
rsd.fetchStudentData();
}
}
Output:
Name: Shubh
Physics Marks: 95
Maths Marks: 100
Chemistry Marks: 90
Total Marks: 285
Percentage: 95.0
Name: Deep
Physics Marks: 80
Maths Marks: 85
Chemistry Marks: 90
Total Marks: 255
Percentage: 85.0Let’s take another example program where we will create a class Employee and we will iterate and display all employee data from the Employee class. So let’s see the following source code.
Program code 3:
package customArrayList3;
import java.util.ArrayList;
public class Employee
{
int eNo;
String name, address;
Employee(int eNo, String name, String address)
{
this.eNo = eNo;
this.name = name;
this.address = address;
}
public Employee()
{
}
// Display all employees data.
void displayData(ArrayList<Employee> list)
{
System.out.println("Employee Detail");
for(Employee emp: list )
{
System.out.println("Employee number: " +emp.eNo);
System.out.println("Employee Name: " +emp.name);
System.out.println("Employee Address: " +emp.address);
}
}
}package customArrayList3;
import java.util.ArrayList;
public class AddingEmployeeData
{
public static void main(String[] args)
{
Employee emp1 = new Employee(102, "Shubh", "Nagpur" );
Employee emp2 = new Employee(205, "Anjali", "Dhanbad");
Employee emp3 = new Employee(333, "Shanjna", "Mumbai");
ArrayList<Employee> list = new ArrayList<Employee>();
list.add(emp1);
list.add(emp2);
list.add(emp3);
Employee temp = new Employee();
// Call displayData method using temp reference variable object and pass list as a parameter.
temp.displayData(list);
}
}Output:
Employee Detail
Employee number: 102
Employee Name: Shubh
Employee Address: Nagpur
Employee number: 205
Employee Name: Anjali
Employee Address: Dhanbad
Employee number: 333
Employee Name: Shanna
Employee Address: MumbaiHope that this tutorial has covered almost all important points related to store user-defined class objects in Java ArrayList. I hope that you will have understood and practiced all example programs.
Thanks for reading!!!
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