What are Objects In Java Programming

 Java Programming Objects

•  Object name in java is a reference
•  References are used to store address 
• All objects created in heap with new statement
•  There is no delete statement in java
• Deletion of object will be handled by garbage collector
• A special value null can be assigned
• Always passed by reference

Object Example
Let Student is a class
Student t; //here t is a reference variable

t=null;     // Assigning a reference to null 

// t=NULL  Error here as  Java  is case sensitive null and NULL are different

t = new Student(); // created in heap
- Alias name can created
for example
Student y=t; // here y and t referring to same object in heap


Parameter Passing

•  Primitives by value
•  Objects by reference

Object as parameter parameter passing by reference
Example 1

class Car{
String make;
String getMake() { return make;}
void setMake(String m){make=m;}

}
class ChangeCarMake{
 static void changeMake(Car p){
  p.setMake("Suzuki");
 }
}
class Test {
public static void main(String o[]){
Car c1=new Car();
c1.setMake("Honda");
ChangeCarMake.changeMake(c1); // passing a reference of class Car System.out.println(c1.getMake());

}
}
output
Suzuki


A program which  Exchange Marks
   
 class Student {
  String name;
  int marks;
  Student ( ) {  }
  Student (String n, int m ){name=n; marks=m;}
  String getName() {return name;}
  int getMarks() {return marks;}
  void setName(String n) {name=n;}
  void setMarks(int m) { marks=m;}
}

  class Test {
static void  exchangeMarks(Student a, Student b){
  int t=a.getMarks();
  a.setMarks(b.getMarks());
  b.setMarks(t);

 }
  public static void main(String o[]){
  Student s1=new Student("Amir",20);
  Student s2=new Student("Imran",90);
  exchangeMarks(s1,s2);
System.out.println(s1.getName() + "  "+ s1.getMarks()); 
System.out.println(s2.getName() + "  "+ s2.getMarks()); 
  }
  }