Encapsulation

package in.ihelpyou;

class Student {

    // private: code outside Student cannot read or change these directly
    private int rollNo;
    private int age;
    private String name;

    public Student(int rollNo, int age, String name) {
        this.rollNo = rollNo;
        this.age = age;
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public String getName() {
        return name;
    }

    // The setter controls every change, so an invalid age can never be stored.
    public void setAge(int age) {
        if (age > 0) {
            this.age = age;
        }
    }

    public void setName(String name) {
        this.name = name;
    }
}

public class School {

    public static void main(String[] args) {

        Student student1 = new Student(10001, 14, "Karthik");
        Student student2 = new Student(10002, 14, "Lakshmi");

        student1.setAge(15);
        student1.setAge(-3);            // ignored by setAge
        student2.setName("Lakshmi S");
        // student1.age = -3;           // compile error: age is private

        System.out.println("Student1 age: " + student1.getAge());    // 15
        System.out.println("Student2 name: " + student2.getName());  // Lakshmi S
    }
}