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In the last lesson we discussed about: Objects and Instances Declaring Variables

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Review. In the last lesson we discussed about: Objects and Instances Declaring Variables The “=“ used as an assignment operator We also looked at the ACM hierarchy. Casting and Precedence.

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Presentation Transcript
slide1

Review

  • In the last lesson we discussed about:
  • Objects and Instances
  • Declaring Variables
  • The “=“ used as an assignment operator
  • We also looked at the ACM hierarchy
slide2

Casting and Precedence

  • When performing arithmetic operations in Java we have to understand how precedence (priority) works.
  • First priority is given to parenthesis ()
  • Second *, /, %
  • Least +,-
  • Starting from left to right
slide3

For example:

  • X = 1 + 3 * 5 / 2;
  • Lets see how this will evaluate.
  • 3 * 5 = 15
  • 15 / 2 = 7 (Integer division)
  • Add 1
  • X=8
slide4

Divide integers but get real

  • int x = 5; (Integer division)
  • double y = x / 2;
  • Evaluates the right side first and then returns the answer to the left side
  • In order to get a double value we will use a process called CAST!
slide5

CAST is just like in a film!

  • Just like a film has a cast of characters who act temporarily to fulfill a role similarly in Java a cast is a conversion of one data type to another.

For e.g.:

int x=5;

double y = (double) x/2 (x remains as an integer)

y now contains 2.5 due to the casting on the right side of the equal sign

slide6

Calculate Average

  • import acm.program.*;
  • public class CalculateAverage extends ConsoleProgram {

public void run() {

println(“This program requires two numbers:”);

int n1 = readInt(“Enter n1”);

int n2 = readInt(“Enter n2”);

double avg = n1 + n2 / 2; //BUGGY!

println(“The average is:” + avg + “.”);

}

  • } // Whats the problem here?
slide7

Short hands

  • Seems like x = x +1 is very commonly used in programming languages
  • There are short hands for doing this:
  • x+=1;
  • x++;
  • x-=1;
  • x--;
  • x*=2;
  • x/=2;
slide8

Constants

  • Lets have a look at an example of area of a circle.
  • double PI =3.14;
  • double A = PI * r * r;
  • PI is a variable and it can be changed which means the whole equation will change.
  • Defining:
  • private static final double PI=3.14;
  • You could come up with a constant called SEVENTY_TWO=72
slide9

Downloading ACM

  • Before beginning to use ACM (Association of Computer Machinery) library you need to download it from:
  • http://www-cs-faculty.stanford.edu/~eroberts/jtf/acm.jar
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