CC438: Exercises I Write down the output and explain

1
CC438 Exercises IWrite down the output and
explain

• public class SwapPrim
• public static void main(String args)
• int x 10
• int y 20
• swap(x, y)
• System.out.println(x " " y)
• public static void swap(int x, int y)
• int tmp x
• x y
• y tmp

2
Write down the output and explain

• public class SwapArray
• public static void main(String args)
• int x new int10, 20
• swap(x)
• System.out.println(x0 " " x1)
• public static void swap(int x)
• int tmp x0
• x0 x1
• x1 tmp

3
Write down the output and explain

• public class Distance
• public static void main(String args)
• // what output do you expect?
• System.out.println(distance(0, 0, 3, 4))
• public static double distance( double x1,
  double y1, double x2, double y2)
• return Math.sqrt((x1 - x2) (x1 - x2)
  (y1 - y2) (y1 - y2))
• Extend this example to work in three dimension
  instead of two
• Think about the possible ways of doing this
  before writing any code
• Hint for a good solution, the method signature
  might need to change

4
Syntax Check

• Which of the following (independent lines) is
  legal?
• int x null
• Integer x null
• int x null
• double x 1
• int x 1.0
• Integer x 1 int y x

5
Sample Exam Question (20)

• Explain the difference between the operator
  and the method equals() in Java. Hence explain
  what the following code would output when the
  main method is run
• public class TestEquals
• public static void main(String args)
• Integer x new Integer(10)
• Integer y new Integer(10)
• System.out.println(x y)
• System.out.println(x.equals(y))
• A a new A(10)
• A b new A(10)
• System.out.println(a.equals(a))
• System.out.println(a.equals(b))
• System.out.println(a b)
• System.out.println(a.equals(x))

6
Sample Question (contd)

• static class A
• int x
• public A(int x) this.x x
• public String toString()
• return "" x
• Write an equals method for class A such that
• new A(x).equals(new Integer(x))
• would return true for any int value of x.