Constructors Using Some Basic Examples in Java

Constructors Using Some Basic Examples:

• Constructors are the special methods whose name is the same as the class name.
• Constructors do not have return types 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 a 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);
 }
}