# In the last lesson we discussed about: Objects and Instances Declaring Variables - PowerPoint PPT Presentation

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

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#### Presentation Transcript

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

• 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

For example:

• X = 1 + 3 * 5 / 2;

• Lets see how this will evaluate.

• 3 * 5 = 15

• 15 / 2 = 7 (Integer division)

• X=8

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!

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

Calculate Average

• import acm.program.*;

• public class CalculateAverage extends ConsoleProgram {

public void run() {

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

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

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

}

• } // Whats the problem here?

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;

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