Constructors Using Some Basic Examples in Java

Constructors Using Some Basic Examples:

• Constructors are the special methods whose name is same as class name.
• Constructors do not have return type even void also.
• Constructors will be invoked by the JVM automatically at the time of object creation.
• Constructors are mainly used to initialize instance variables of class with different set of values.

Examples:

Lab1.java

class Lab1
{
    public static void main(String args[])
  {
        Student stu1 = new Student();
        stu1.show();
        Student stu2 = new Student();
        stu2.show();
    }
}
class Student
{
    intsid;
    String sname;
    void show()
  {
        System.out.println(sid + "\t" + sname);
    }
}

Lab2.java

class Lab2
{
    public static void main(String args[])
  {
        Student stu = new Student();
        stu.sid = 99;
        stu.sname = "Ayush";
        stu.show();
    }
}
class Student
{
    intsid;
    String sname;
    void show()
    {
        System.out.println(sid + "\t" + sname);
    }
}

Lab3.java

class Lab3
{
    public static void main(String args[])
  {
        Student stu = new Student();
        stu.sid = 99;
        stu.sname = "Ayush";
        stu.show();
    }
}
class Student
{
    intsid;
    String sname;
    Student()
  {
        System.out.println("Student Default Constructor");
    }
    void show()
  {
        System.out.println(sid + "\t" + sname);
    }
}

Lab4.java

class Lab4
{
    public static void main(String args[])
  {
        Student stu = new Student();
        stu.sid = 99;
        stu.sname = "Ayush";
        stu.show();
    }
}
class Student
{
    intsid;
    String sname;
    Student(int id, Stringsn)
  {
        System.out.println("Student 2-Arg Constructor");
        sid = id;
        sname = sn;
    }
    void show()
  {
        System.out.println(sid + "\t" + sname);
    }
}

Lab5.java

class Lab5
{
    public static void main(String args[])
  {
        Student stu1 = new Student(88, "Ayush");
        stu1.show();
        Student stu2 = new Student(99, "Garg");
        stu2.show();
    }
}
class Student
{
    intsid;
    String sname;
    Student(int id, Stringsn)
  {
        System.out.println("Student 2-Arg Constructor");
        sid = id;
        sname = sn;
    }
    void show()
  {
        System.out.println(sid + "\t" + sname);
    }
}

Lab6.java

class Lab6
{
    public static void main(String args[])
  {
        Student stu1 = new Student();
        stu1.show();
        Student stu2 = new Student(99, "Garg");
        stu2.show();
    }
}
class Student
{
    intsid;
    String sname;
    Student()
  {
        System.out.println("Student Default Constructor");
    }
    Student(int id, Stringsn)
  {
        System.out.println("Student 2-Arg Constructor");
        sid = id;
        sname = sn;
    }
    void show()
  {
        System.out.println(sid + "\t" + sname);
    }
}

Lab7.java

class Lab7
{
    public static void main(String args[])
  {
        Student stu1 = new Student(99, "Ayu", "[email protected]", 9999);
        stu1.show();
        Student stu2 = new Student(88, "sh", "[email protected]");
        stu2.show();
        Student stu3 = new Student(77, "AG");
        stu3.show();
        Student stu4 = new Student();
        stu4.show();
    }
}
class Student
{
    intsid;
    String sname;
    String email;
    long phone;

    Student(int id, Stringsn, Stringem, longph)
  {
        System.out.println("Student 4-Arg Constructor");
        sid = id;
        sname = sn;
        email = em;
        phone = ph;
    }
    Student(int id, Stringsn, Stringem)
  {
        System.out.println("Student 3-Arg Constructor");
        sid = id;
        email = em;
        sname = sn;
    }
    Student(int id, Stringsn)
  {
        System.out.println("Student 2-Arg Constructor");
        sid = id;
        sname = sn;
    }
    Student()
  {
        System.out.println("Student Default constructor");
    }
    void show()
  {
        System.out.println(sid + "\t" + sname + "\t" + "email" + "phone");
    }
}

Lab8.java

class Lab8
{
    public static void main(String args[])
  {
        Student stu3 = new Student(77, "AG");
        stu3.show();
    }
}
class Student
{
    intsid;
    String sname;
    Student(int id, Stringsn)
  {
        System.out.println("Student 2-Arg Constructor");
        sid = id;
        sname = sn;
    }
    Student(int x, int y)
  {
        System.out.println("Student 2-Arg constructor");
        sid = x;
        sname = y;
    }
    void show()
  {
        System.out.println(sid + "\t" + sname);
    }
}

Lab9.java

class Lab9
{
    public static void main(String args[])
    {
        Student stu3 = new Student(77, "AG");
        stu3.show();
    }
}
class Student
{
    intsid;
    String sname;
    Student(int id, Stringsn)
  {
        System.out.println("Student 2-Arg Constructor");
        sid = id;
        sname = sn;
    }
    Student(String y, int x)
  {
        System.out.println("Student 2-Arg constructor");
        sname = y;
        sid = x;
    }
    void show()
  {
        System.out.println(sid + "\t" + sname);
    }
}

Lab10.java

class Lab10
{
    public static void main(String args[])
  {
        Student stu = new Student();

        stu.Student(77, "AG");
        stu.show();
    }
}
class Student
{
    intsid;
    String sname;
    Student(int id, Stringsn)
  {
        System.out.println("Student 2-Arg Constructor");
        sid = id;
        sname = sn;
    }
    Student()
  {
        System.out.println("Student default constructor");
    }
    void show()
  {
        System.out.println(sid + "\t" + sname);
    }
}

Lab11.java

class Lab11
{
    public static void main(String args[])
  {
        Student stu = new Student();
        stu.Student(77, "AG");
        stu.show();
    }
}
class Student
{
    intsid;
    String sname;
    void Student(int id, Stringsn)
  {
        System.out.println("Student 2-Arg Constructor");
        sid = id;
        sname = sn;
    }
    Student()
  {
        System.out.println("Student default constructor");
    }
    void show()
  {
        System.out.println(sid + "\t" + sname);
    }
}

Lab12.java

class Lab12
{
    public static void main(String args[])
  {
        Student stu = new Student();
        stu.Student(77, "AG");
        stu.show();
    }
}
class Student
{
    intsid;
    String sname;
    void Student(int id, Stringsn)
  {
        System.out.println("Student 2-Arg Constructor");
        sid = id;
        sname = sn;
    }
    void show()
  {
        System.out.println(sid + "\t" + sname);
    }
}

Lab13.java

class Lab13
{
    public static void main(String args[])
  {
        Student stu = new Student(-12);
        stu.show();
    }
}
class Student
{
    int age = 18;
    Student(int ag)
    {
        System.out.println("Student 2-Arg Constructor");
        age = ag;
    }
    void show()
    {
        System.out.println(age);
    }
}

Lab14.java

class Lab14
{
    public static void main(String args[])
  {
        Student stu = new Student(-12);
        stu.show();
    }
}
class Student
{
    int age = 18;
    Student(int ag)
    {
        System.out.println("Student 2-Arg Constructor");
        if (ag = 18)
            return;
        age = ag;
    }
    void show()
    {
        System.out.println(age);
    }
}

Lab15.java

class Lab15
{
    public static void main(String args[])
  {
        Student stu = new Student(-12);
        stu.show();
    }
}
class Student
{
    int age = 18;
    Student(int ag)
    {
        System.out.println("Student 2-Arg Constructor");
        if (ag = 18)
            return 0;
        age = ag;
    }
    void show()
    {
        System.out.println(age);
    }
}