Java Example: Data Encapsulation http://www.chankok.com/java-data-encapsulation/

DataEncapsulationExample.java

package com.chankok.oop;

public class DataEncapsulationExample {

    public static void main(String[] args) {

        try {

            Student student1 = new Student();
            student1.setName("Chankok");
            student1.setSubject("History");
            student1.setMarks(-1);

            System.out.println("Student 1 Name: " + student1.getName());
            System.out.println("Student 1 Subject: " + student1.getSubject());
            System.out.println("Student 1 Marks: " + student1.getMarks());

            Student student2 = new Student();
            student2.setName(null);
            student2.setSubject("Mathematics");
            student2.setMarks(50);

            System.out.println("Student 2 Name: " + student2.getName());
            System.out.println("Student 2 Subject: " + student2.getSubject());
            System.out.println("Student 2 Marks: " + student2.getMarks());

        } catch (Exception e) {
            e.printStackTrace();
        }

    }

}

Student.java

package com.chankok.oop;

public class Student {

    private String name;
    private String subject;
    private int marks;

    public Student() {
        this.name = "Default Student Name";
    }

    public String getName() {
        return name;
    }

    public void setName(String name) throws Exception {
        if (name == null) {
            // Not allow to set student name as null value
            throw new IllegalArgumentException("Student name cannot be null");
        }
        this.name = name;
    }

    public String getSubject() {
        return subject;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }

    public int getMarks() {
        return marks;
    }

    public void setMarks(int marks) {
        if (marks < 0) {
            // Not allow to set student marks as negative value, assign default value
            this.marks = 0;
        } else {
            this.marks = marks;
        }
    }

}