More on 1-D Array

1
More on 1-D Array

• Overview
• Array as a return type to methods
• Array of Objects
• Array Cloning
• Preview 2-D Arrays

2
Array as return type to methods

• We saw in the last lecture, that arrays can be
  passed as parameters to methods.
• In addition, methods can return array as their
  result a reference to an array object.
• import java.io.
• class ArrayAndMethods
• static BufferedReader stdin new
  BufferedReader( new InputStreamReader(System.in))
  
• public static void main(String args) throws
  IOException
• int size
• System.out.print("Enter array size ")
• size Integer.parseInt(stdin.readLine())
• double firstArray createArray(size)
• double secondArray createArray(size)
• System.out.println("The dot product
  "dotProduct(firstArray, secondArray))

3
Array as return type to methods

• static double createArray(int size) throws
  IOException
• double array new doublesize
• System.out.println("Enter "size" elements
  for this array ")
• for (int i0 iltsize i)
• arrayi Double.parseDouble(
  stdin.readLine())
• return array
• static double dotProduct(double first,
  double second)
• double sum 0
• for (int i0 iltfirst.length i)
• sum firstisecondi
• return sum

4
Array of Objects

• In the examples we have seen so far, we have been
  creating arrays whose elements are primitive
  types.
• We can equally create an array whose elements are
  objects.
• Assuming we have a class named Student, then we
  can create an array, students, to hold 10 Student
  objects as follows
• Student students new Student10

5
Array of Objects (contd)

• As you can see from the figure, there is a
  fundamental difference between an array of
  primitive type and an array of object.
• Here, the array only holds references to the
  actual objects.
• The statement
• Student students new Student10
• only creates the references. To actually create
  the objects, we have to use the new operator,
  usually is a loop as follows
• for (int i 0 i lt students.length
  i) studentsi new Student(id, grade)
• The following is the complete Student example.
• class Student
• int iDNumber
• double grade
• public Student(int iDNumber, double grade)
• this.iDNumber iDNumber
• this.grade grade
• public void print()
• System.out.println(iDNumber"\t"grade)

6
Array of Objects (contd)

• import java.io
• public class ArrayOfObjects
• static BufferedReader stdin new
  BufferedReader( new InputStreamReader(System.in))
  
• public static void main(String args) throws
  IOException
• int size
• System.out.print("Enter number of
  students ")
• size Integer.parseInt(stdin.readLine())
  
• Student students createArray(size)
• double average average(students)
• System.out.println("The average is
  "average)
• System.out.println("Students below
  average are")
• for (int i0 iltstudents.length i)
• if (studentsi.grade lt average)
• studentsi.print()

7
Array of Objects (contd)

• static Student createArray(int size) throws
  IOException
• Student array new Studentsize
• int id
• double grade
• System.out.println("Enter "size"
  students")
• for (int i0 iltsize i)
• System.out.print("ID Number ")
• id Integer.parseInt(stdin.readLi
  ne())
• System.out.print("Grade ")
• grade Double.parseDouble(
  stdin.readLine())
• arrayi new Student(id,
  grade)
• return array
• static double average(Student studentList)
  
• double sum 0
• for (int i0 iltstudentList.length
  i)
• sum studentListi.grade
• return sum/studentList.length

8
Array cloning

• The following example shows how we may make a
  copy of an array. This is called clonning.
•  
• class ArrayCloningExample
•   public static void main (String args)
• int a new int5
• int b
• int i
• System.out.println("Contents of a")
• for(i 0 i lt a.length i)
• ai i i
• System.out.println("i "i"
  a"i"\t" ai)
• b (int ) a.clone()
•   System.out.println("Contents of b
  immediately after duplication from a")
• for(i 0 i lt b.length i)
• System.out.println("i "i" b" i "
  \t" bi)
•   for(i 0 i lt b.length i)
• bi 2
• System.out.println("Contents of a and b
  after doubling elements of b")

9
Array cloning (contd)

• for(i 0 i lt b.length i)
• System.out.println("i " i " a"
  i " \t"ai"\t\tb" i " \t"
  bi)
• Sample Output
• Contents of a
• i 0 a0 0
• i 1 a1 1
• i 2 a2 4
• i 3 a3 9
• i 4 a4 16
• Contents of b after duplication from a
• i 0 b0 0
• i 1 b1 1
• i 2 b2 4
• i 3 b3 9
• i 4 b4 16
• Contents of a and b after doubling elements
  of b
• i 0 a0 0 b0 0