Programming Review

Java Class Structure

All Java statements are part of a classpublic class ClassName{

}

What’s inside a classprivate instance variables - attributesmethods – behaviors

public class Rectangle{

// declare instance variablesprivate int length;private int width;private int perimeter;

// define methodspublic void setLengthAndWidth(int len, int wid){

length = len;width = wid;

}……

To run a program

Must have a class that has a main method

public static void main(String[] args){

program statements;}

Declaring variables

Variables store primitive data or addresses

primitives – built in data typesint, long, byte, double, char …

addresses – myScanner, myRectangle…Java is strongly typed – must declare variables

before usingint age; // declaration that will store an

integerdouble price // declaration that will

store adecimal value

Java Identifiers

Java namesletters, numbers, underscore, $can not start with numberClass names start with cap

MyClassVariable names start lowercase

calculatePerimeter

Assigning values

Assignment operator= var1 = 15; var2 = var1;

Compound operators+= -= *= /= %=

var1 = var1 + 5 same as var1+=5

Increment and Decrement operators

Increment (increase by 1)pre ++x; increment x then usepostx++; use x then increment

Decrement (decrease by 1)pre --x; decrement x then use

x++; use x then decrement

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average = total / 5sum = one + two

Expressions usually consist of operators, variables, and/or values.

String Concatenation

String literal “This is a String”

+ concatenates string and primitiveseg. String s1 = “This is my string.”

String s2 = “ I will print it “String s3 = “ times”int times = 2;

System.out.println(s1 + s2);This is my string I will print it.

System.out.println(s1 + s2 + times + s3);This is my string. I will print it 2 times

Writing CodeExample one: given existing code

given variables, use to solve problem

Given double priceONe, priceTwo, priceThree

double totalPrice, averagePriceWrite statements that assign values to each price,calculate and store total price, and calculate averge.Output to screen:

Price one: xx.xxPrice two: xx.xxPrice three: xx.xxTotal price: xx.xxAverage price: xx.xx

Don’t redeclare or create new variables here !

Use those givenpriceOne = 3.00;priceTwo = 14.50;priceThree = 2.99;

totalPrice = priceOne + priceTwo + priceThree;averagePrice = totalPrice / 3;

Output statements

System.out.println(“Price one:\t” + priceOne;System.out.println(“Price two:\t” + priceTwo;System.out.println(“Price three:\t” +

priceThree;System.out.println(“Total price:\t” +

totalPrice;System.out.println(“Average price:\t” +

averagePrice;

Writing a program based on requirements

First read and understand program requirementsEg. Write a program that declares variables to store three test grades. Grades are recorded as integers. Calculate and store the average grade as a real number. Print each grade separated by a comma on one line and a line that looks like the following on the next:

The average grade is xx.xx (where xx.xx is calculated value)

Name your program MyAverage.

What’s first?Since we are writing a complete program, we

know we need the basic java class and a main method. At least start those.public class MyAverage{

public static void main(String[] args){

// leave lots of space for statements

}}

What’s next?We know that all statements should be in a

methodSo think about the storage you need and declare

variables of the right type.

We need variables that would hold each grade and the requirements state that the grades are integers. Declare those variable inside main.public class MyAverage{

public static void main(String[] args){

int grade1, grade2, grade3;// notice that it was not a requirement

to assign values.

}}

What’s next?The requirements state that the average has

to be calculated and stored, so we need a variable of the right type.public class MyAverage{

public static void main(String[] args){ int grade1, grade2, grade3; double average;}

}

What’s next?Now that all variables are declared, perform

calculations using java expressions.// Note: grades must be assigned a value or read in// at runtimeaverage = (grade1 + grade2 + grade3) / 3.0;

With all values stored in memory, we can now print.

System.out.println(grade1 + “,” + grade2 + “,”+grade3);

System.out.println(“The average grade is “ + average);