Java Fundamentals MIS 3023 Business Programming Concepts II The University of Tulsa Professor: Akhilesh Bajaj

All slides in this presentation ©Akhilesh Bajaj, 2006. All rights reserved

Objectives

• Understand the building blocks of programs • Learn the basic Java TM types • Take another look at our first lab Let’s get started!

Building Blocks of Programming

• Data & Instructions are the 2 fundamental building blocks. •

Data:

Types & Variables •

Instructions:

Control structures & subroutines

Data:

A

type

is the set of possible values that a variable of that type can contain.

E.g.,

what values can a variable of type

int

contain?

A

variable

is a label or a name for a main memory location.

Memory maps:

Maps of the main memory of the process as it executes, showing the data being used by the process.

Building Blocks of Programming

•

Instructions:

Control structures & subroutines • Control structures manage the

“flow of control”.

The basic structures are:

branching

(if, switch) and

looping

(for, while, do-while). • Subroutines are used to

chunk

tasks. We divide the overall task our program needs to perform into chunks, and then label each chunk with the name of the subroutine. In Java, subroutines are called

methods.

In C/C++ they are called

functions.

In BASIC, they are called

subroutines.

In Pascal, they are called

procedures

and

functions.

• It’s very important to plan the program so that it is broken into

meaningful

chunks.

Rules of thumb for chunking:

a) If we are typing the same code again and again, we should write it in a

method

, and then call the

method

by name in the program. b) If it helps us solve the

overall

problem by assuming a certain part is already taken care of in the method, without worrying about how, then that certain part can be coded as a subroutine or

method

and called in the program.

Basic Types in Java

• Java is strongly typed. Primitive Types: These are the building blocks for more complex types.

Type Bit Values Size boolean char 8 16 true , false ‘\u0000’ to ‘\uFFFF’ byte short int long float double 8 16 32 64 32 64 Standard ISO Unicode Char Set -128 to + 127 -32,768 to +32,767 -2,147,483,648 to +2,147,483,647 -9,223,372,036,854,775,808 to + (that -1) -3.40292347E+38 to + that -1.79769313486231570E+308 to + that IEEE 754 floating point IEEE 754 floating point

Basic Types in Java

• The most common numerical types we will use are:

int

for integers,

double

for decimal points • For char constants, put a

single character in single quotes

. The Unicode char set contains 65,536 characters, in other words all chars in all written languages. 255 chars in this scheme are ASCII. So we just put whatever character we want in single quotes, as a char constant.

The following special character values can be used: ‘\b’ backspace ‘\t’ tab ‘\n’ linefeed ‘\r’ carriage return \'' double quote (a single quote will give us a single quote) \\ backslash

Note: ‘3’ is a char, 3 is a numeric literal, ‘a’ is a char, a is a variable name.

“Akhilesh” is a String.

Basic Types in Java

•

String:

This is not a primitive type in Java. However, it is used so often, that we need to look at it right away. A String is a

class

in the standard Java library.

A class is more complex than a type.

We create variables of types But we create objects of classes .

We create objects of class String , every time we need a String. Each object we create has a

name

,

data

(the actual string of characters) and certain operations (

methods)

that we can use on that object. String greeting = “Hello”; String emptyStr = “”; //an empty string System.out.println(greeting + ‘\n’); Prints out Hello and then a new line. List of useful methods for String class in our text book: \\bahweb\nfp\bajaja\MIS3023\Text\javanotes4.1\c2\s3.html

Basic Types in Java

•

String:

We do not need to understand how these object methods work. We use them as

black boxes

. A lot of the power of Java is the API (Application Programming Interface) which consists of a lot of classes that we can use, without really looking at the code that went into them. www.java.sun.com

lists the current API for Java. Classes can have two types of methods in Java: a) A class can have

static methods

that are called by Classname.methodname(any parameters) b) A class can have

non-static methods

that

need an object created first

of that class, and then they can be used. The String methods we saw are

non-static

. println() method called on class System.out

is a static without declaring an object of that class.

Revisiting our First Lab

Import hints to Java compiler where to look for classes we are using We write every file as a class. The file name we save it as MUST be the same as the class name with a .java

extension. Each program has a main() method that is run first. In this example, that is the ONLY method. The println() method is a static method in the of the System class. out class, which is a subclass import java.io.*; public class HelloWorld { // A program to display the message // "Hello World!" on standard output { public static void main(String[] args) System.out.println("Hello World!"); } } // end of class HelloWorld

Fun In Class Assignment

Let us think about a car payment calculator program, to help a car dealership’s customers decide how much they can pay. • What variables (data) do we need to solve the problem?

• What flow (process) do we need to solve the problem?

Write a sketch of the program on paper.

CONCLUSION

•

We took a look at the basic building blocks of programming

•

We learnt basic types and the String Class Chapter 2, section 2 in our book has more explanation: http://nfp.cba.utulsa.edu/bajaja/mis3023/Text/javanotes4.

1/c2/s2.html

•

We began to understand classes and how they work