Passing and returning non primitive values from methods
Introduction:
In Java, all primitives are passed by value. This means a copy of the value is passed into the method. Objects can be passed natively, just like primitives. It is often misstated that Object parameters are passed by Reference. While it is true that the parameter is a reference to an Object, the reference itself is passed by Value.
Lab Activities:
Activity 1:
Passing object as parameter and change value of its data member.
Solution:
public class ObjectPass
{
public int value;
public static void increment(ObjectPass a)
{
a.value++;
}
}
Public class ObjectPassTest
{
public static void main(String[] args)
{
ObjectPass p = new ObjectPass(); p.value = 5;
System.out.println(“Before calling: ” + p.value); increment(p);
System.out.println(“After calling: ” + p.value);
}
}
Output:
Before calling: 5
After calling: 6
Now it is like the pass was by reference! but the thing is what we pass exactly is a handle of an object, and in the called method a new handle created and pointed to the same object. Now when more than one handles tied to the same object, it is known as aliasing. This is the default way Java does when passing the handle to a called method, create alias.
Activity 2:
The following activity demonstrates the creation of a method that accepts and returns object.
Solution:
public class Complex
{
Private double real;
Private double imag;
Public Complex()
{ real = 0.0; imag = 0.0; }
Public Complex (double r, double im)
{ real = r; imag = im; }
Public Complex Add (Complex b)
{
Complex c_new = new Complex (real + b.real, imag+ b.imag); returnc_new;
}
Public Show ()
{
System.out,println( real + imag);
}
}
Public class ComplexTest
{
void main()
{
Complex C1 = new Complex(11, 2.3); Complex C2 = new Complex(9, 2.3); Complex C3 = new complex();
C3 = C1.Add(C2);
write(C3).show();
}
}
Activity 3:
The following activity demonstrates the creation of a method that accepts two objects.
public class Point
{
private int X; private int Y; public Point()
{
X = 5;
Y = 6;
}
public Point(int a, int c)
{
X = a; Y = c;
}
public void setX (int a)
{
X = a;
}
public void setY (int c)
{
Y= c;
}
public int getX()
{
return X;
}
public int getY(){
return Y;
}
public Point Add(Point Pa, Point Pb )
{
Point p_new = new Point(X+ Pa.X + Pb.X, Y+ Pa.Y + Pb.Y); return p_new;
}
public void display()
{
System.out.println(X); System.out.println(Y);
}
}
public class PointTest
{
public static void main(String[] args)
{
Point p1 = new Point(10,20); Point p2 = new Point (30,40); Point p3 = new Point (); Point p4 = p1.Add(p2,p3); p4.display();
}
}
Home Activities:
Activity 1:
Create a class ― Distance‖ with two constructors (no argument, and two argument), two data members ( feet and inches) . Create setter, getter and display method. Create a method that adds two Distance Objects and returns the added Distance Object.
Activity 2:
Create an Encapsulated class Book. Its data members are
- author (String)
- chapterNames[100] (String[])
Create two overloaded constructors, one with no argument and one with two arguments.
Create a method compareBooks that compares the author of two Books and returns true if both books have same author and false otherwise. (This method must manipulate two Book objects)
Create a method compareChapterNames that compares the chapter names of two Books and returns the book with larger chapters. Display the author of the book with greater chapters in main.
Create a runner class that declares two objects of type Book. One object should be declared using no argument constructor and then the parameters should be set through the set() methods. The second object should be declared with argument constructor. Finally the CompareBooks()and compareChapterNames method should be called and the result should be displayed in the runner class.
Assignment:
Define a class called Fraction. This class is used to represent a ratio of two integers. Create two constructors, set, get and display function. Include an additional method, equals, that takes as input another Fraction and returns true if the two fractions are identical and false if they are not.
