Introduction to JAVA Programming Basics PROGRAMMING STEPS ANALISA MASALAHNYA INPUT-NYA APA SAJA? ALGORITMA PROSESNYA BAGAIMANA? OUTPUT-NYA APA? KETIK SOURCE CODE-NYA HEADER FILES import < library > GLOBAL SECTIONS VARIABEL GLOBAL, FUNGSI BANTU MAIN SECTIONS VARIABEL LOKAL, INPUT, PROSES, OUTPUT COMPILE & RUN PROGRAMNYA ADA ERROR ? TES HASILNYA SUDAH BENAR ? BUAT ARSIP/ DOKUMENTASINYA Computers and Programming A computer is a machine that can process data by carrying out complex calculations quickly. A program is a set of instructions for the computer to execute. A program can be high-level (easy for humans to understand) or low-level (easy for the computer to understand). In any case, programs have to be written following a strict language syntax. Running a Program Typically, a program source code has to be compiled into machine language before it can be understood by a computer. writes programmer void test() { println(“Hi”); } source code (high level) compiler machine language Hi executed by object code (low level) computer Portability Different makes of computers speak different “languages” (machine language) use different compilers. This means that object code produced by one compiler may not work on another computer of a different make. Thus the program is not portable. Java is portable because it works in a different way. History of Java The Java programming language was developed at Sun Microsystems It is meant to be a portable language that allows the same program code to be run on different computer makes. Java program code is translated into bytecode that is interpreted into machine language that the computer can understand. Java Byte-Code Java source code is compiled by the Java compiler into byte-code. Byte-code is the machine language for a ‘typical’ computer. This ‘typical’ computer is known as the Java Virtual Machine. A byte-code interpreter will translate byte-code into object code for the particular machine. The byte-code is thus portable because an interpreter is simpler to write than a compiler. Running a Java Program writes programmer public void test() { System.out.println(“Hi”); } Java source code (high level) Java compiler Java byte-code Extra step that allows for portability Byte-code interpreter Machine language Hi executed by object code (low level) computer Types of Java Programs Console Applications: Simple text input / output This is what we will be doing for most of this course as we are learning how to program. public class ConsoleApp { public static void main(String[] args) { System.out.println("Hello World!"); } } Types of Java Programs GUI Applications: Using the Java Swing library import javax.swing.*; public class GuiApp { public static void main(String[] args) { JOptionPane.showMessageDialog(null, "Hello World!", "GUI Application", JOptionPane.INFORMATION_MESSAGE); System.exit(0); } } Types of Java Programs Applets To be viewed using a internet browser import java.applet.*; import java.awt.*; public class AppletEg extends Applet { public void paint(Graphics g) { g.drawString("Hello World!", 20, 20); } } ___________________________________________________ <applet code="AppletEg.class" width=200 height=40> </applet> Sample Java Program public class CalcCircle { public static void main(String[ ] args) { int radius; // radius - variable final double PI = 3.14159; // PI - constants radius = 10; double area = PI * radius * radius; double circumference = 2 * PI * radius; System.out.println(”For a circle with radius ” + radius + ”,”); System.out.print(”The circumference is ” + circumference); System.out.println(” and the area is ” + area); } } Elements of a Java Program A Java Program is made up of: Identifiers: variables constants Literal values Data types Operators Expressions Identifiers/ Pengenal The identifiers in the previous program consist of: identifier indicating name of the program (class name) public class CalcCircle { public static void main(String[] args) { int radius; // radius - variable final double PI = 3.14159; // PI - constants … untuk identifier } menyimpan nilai radius } (variable) identifier untuk menyimpan nilai tetap PI (constant) Data Types/ Tipe Data Data types indicate the type of storage required. public class CalcCircle { public static void main(String[ ] args) PI adalah sebuah nilai floating-point (double) { int radius; // radius - variable final double PI = 3.14159; // PI - constants } } … adalah sebuah nilai integer (int) radius Literal values Literals are the actual values stored in variables or used in calculations. public class CalcCircle { public static void main(String[ ] args) the variable radius stores the value 10 { … radius = 10; … } } Operators and Expressions Operators allow us to perform some calculations on the data by forming expressions. public class CalcCircle Sebuah ekspresi yang { public static void main(String[ ] args) menggunakan { operators dan operands … double area = PI * radius * radius; double circumference = 2 * PI * radius; … } Operator perkalian (*) dipakai } Untuk menghitung luas bidang Java Program Structure For the next few weeks, our Java programs will have the following structure: Program berupa definisi class. Gunakan nama class yang sama dengan nama file-nya. Misal CalcCircle.java public class CalcCircle { public static void main(String[ ] args) { Program harus memiliki method // This section consists of main sebagai titik awal eksekusi // program code consisting of program. // of Java statements // } Kurung kurawal menunjukkan awal dan akhir. } Gunakan indentasi supaya jelas dibaca. Displaying Output For console applications, we use the System.out object to display output. public class CalcCircle { public static void main(String[ ] args) { … System.out.println(”For a circle with radius ” + radius + ”,”); System.out.print(”The circumference is ” + circumference); System.out.println(” and the area is ” + area); } } Teks dan data diantara tanda petik akan ditampilkan di layar monitor. Compiling and Running The preceding source code must be saved as CalcCircle.java You must then use the Java Development Kit (JDK) to compile the program using the command javac CalcCircle.java The byte-code file CalcCircle.class will be created by the compiler if there are no errors. To run the program, use the command java CalcCircle Compiling and Runnng Buttons to compile and run the program Anatomy of a Java Class A Java console application must consist of one class that has the following structure: /* This is a sample program only. Written by: Date: */ class header public class SampleProgram { public static void main(String [] args) { int num1 = 5; // num stores 5 System.out.print("num1 has value "); System.out.println(num1); } } main method Anatomy of a Java Class A Java console application must consist of one class that has the following structure: /* This is a sample program only. Written by: multi-line comments Date: */ name of the class public class SampleProgram { public static void main(String [] args) { in-line statements int num1 = 5; // num stores 5 comments System.out.print("num1 has value "); to be System.out.println(num1); executed } } What is the result of execution? public class CalcCircle { public static void main(String[ ] args) { int radius; // radius - variable final double PI = 3.14159; // PI - constants radius = 10; double area = PI * radius * radius; double circumference = 2 * PI * radius; System.out.println(”For a circle with radius ” + radius + ”,”); System.out.print(”The circumference is ” + circumference); System.out.println(” and the area is ” + area); } } Displaying output There are some predefined classes in Java that we can use for basic tasks such as: reading input displaying output We use the System class to display output to the screen for console applications. System.out is an object that provides methods for displaying strings of characters to the console screen. The methods we can use are print and println. Example Write a program that prints two lines: I love Java Programming It is fun! public class PrintTwoLines { public static void main(String[] args) { System.out.println("I love Java Programming"); System.out.println("It is fun"); } } Print vs Println What if you use System.out.print() instead? System.out.println() advances the cursor to the next line after displaying the required output. If you use System.out.print(), you might need to add spaces to format your output clearly. Examples Code Fragment Output Displayed System.out.println("First line"); System.out.println("Second line"); First line Second line System.out.print("First line"); System.out.print("Second line"); First lineSecond line Exercise Write a Java program that displays your name and your studentID. // Sandy Lim // Lecture 1 // Printing name and student ID public class Information { public static void main (String[] args) { // your code here } } Exercise Write a Java program that prints out to the screen the following tree: // Sandy Lim * // Lecture 1 // Printing a tree using * *** public class tree { ***** public static void main (String[] ******* { // your code here ******* } } ***** args) Reminders Get your computer accounts before next week's tutorial so that you can start programming ASAP. Download JCreatorLE and J2SDK1.5.0, you can access both through the JCreator (3.50LE) website: http://www.jcreator.com/download.htm Data Types, Variables & Operators Memory and Data Salah satu komponen penting komputer adalah memory. Memori komputer menyimpan: data yang akan diproses data hasil dari sebuah proses Dapat kita bayangkan bahwa sebuah memori komputer tersusun atas kotak-kotak/ laci untuk menyimpan data. Ukuran kotak akan tergantung pada tipe data yang dipakai. Identifiers Kita harus memberi nama untuk setiap kotak memori yang kita pakai untuk menyimpan data. Nama itulah yang dikenal sebagai nama variabel, atau identifiers. Data asli adalah nilai literal dari identifier. BIT106 The box is identified as subject and it stores the value “BIT106” subject value of subject identifier / variable name Java Spelling Rules An identifier can consist of: Sebuah identifier dapat tersusun dari: Letters/ huruf (A – Z, a – z) Digits/ angka (0 to 9) the characters/ karakter _ and $ The first character cannot be a digit. Karakter pertama tidak boleh sebuah angka. Identifier Rules A single identifier must be one word only (no spaces) of any length. Sebuah identifier harus berupa satu kata (tanpa spasi) dengan panjang berapapun. Java is case-sensitive. Reserved Words cannot be identifiers. These are words which have a special meaning in Java Kata-kata yang telah memiliki makna khusus dalam bahasa Java Examples Examples of identifiers num1 num2 first_name lastName numberOfStudents accountNumber myProgram MYPROGRAM Examples of reserved words public if int double see Appendix 1 in the text book for others. Illegal identifiers 3rdValue my program this&that Exercise Which of the following are valid identifier names? my_granny’s_name joesCar integer 2ndNum Child3 double third value mid2chars PUBLIC Types of Data What kind of data can be collected for use in a computer system? Data jenis apakah yang dapat dikumpulkan untuk pemakaian sebuah sistem komputer? Consider data on: College application form/ Formulir SPMB Student transcript/ Transkrip mahasiswa Role Playing Game (RPG) Types of Data We typically want to collect data which may be numeric characters Strings choice (Y/N) Java Data Types In order to determine the sizes of storage (boxes) required to hold data, we have to declare the data types of the identifiers used. Untuk menetukan ukuran penyimpanan (kotak) yang diperlukan untuk menyimpan data, maka kita perlu mendeklarasikan tipe data yang dipakai oleh identifier. Integer data types are used to hold whole numbers 0, -10, 99, 1001 The Character data type is used to hold any single character from the computer keyboard '>', 'h', '8' Floating-point data types can hold numbers with a decimal point and a fractional part. -2.3, 6.99992, 5e6, 1.5f The Boolean data type can hold the values true or false. Primitive vs Reference Data Types A data type can be a: Primitive type Reference type (or Class type) Primitive vs Reference Data Types A Primitive type is one that holds a simple, indecomposable value, such as: a single number a single character A Reference type is a type for a class: it can hold objects that have data and methods Java Primitive Data Types There are 8 primitive data types in Java Type name Kind of value Memory used byte integer 1 byte short integer 2 bytes int integer 4 bytes long integer 8 bytes float floating-point number 4 bytes double floating-point number 8 bytes char single character 2 bytes boolean true or false 1 bit Declaring variables When we want to store some data in a variable, we must first declare that variable. to prepare memory storage for that data. Syntax: Type VariableName; Declaring variables Examples: The following statements will declare an integer variable called studentNumber to store a student number: a double variable to store the score for a student a character variable to store the lettergrade public static void main(String[] args) { // declaring variables int studentNumber; double score; char letterGrade; Assignment Statements Once we have declared our variables, we can use the variables to hold data. This is done by assigning literal values to the variables. Syntax (for primitive types): VariableName = value; This means that the value on the right hand side is evaluated and the variable on the left hand side is set to this value. Masukkan value ke VariableName Assignment Statements Examples: Setting the student number, score and lettergrade for the variables declared earlier: public static void main(String[] args) { // declaring variables int studentNumber; double score; char letterGrade; // assigning values to variables studentNumber = 100; score = 50.8; letterGrade = 'D'; } Initializing Variables We may also initialize variables when declaring them. Syntax: Type VariableName = value; This will set the value of the variable the moment it is declared. This is to protect against using variables whose values are undetermined. Initializing Variables Example: the variables are initialized as they are declared: public static void main(String[] args) { // declaring variables int studentNumber = 100; double score = 50.8; char letterGrade = 'D'; } Arithmetic Operators We can use arithmetic operators in our assignment statements. The Java arithmetic operators are: addition, + (integer and floating-point) subtraction, (integer and floating-point) multiplication, * (integer and floating-point) division, / (integer and floating-point) modulus, % (integer division to find remainder) Arithmetic Operators Example: using the + operator public static void main(String[] args) { // declaring two integer variables int num1 = 5, num2 = 8; // declaring a variable to store the total int total; // performing addition: total = num1 + num2; // display result System.out.println(“total = “ + total); } Arithmetic Expressions More examples of expressions: public static void main(String[] args) { // declaring variables int num1 = 5, num2 = 8; int quotient, remainder; double total, average; // performing arithmetic: total = num1 + num2; average = total / 2; // floating-point division quotient = num1 / num2; //integer division remainder = num1 % num2; // how to display the results? } Operator Precedence Operators follow precedence rules: Thus you should use parentheses ( ) where necessary. Generally according to algebraic rules: (),*,/,%,+,- Operator Precedence Example: The expressions 3 + 5 * 5 will evaluate to 28 (3 + 5) * 5 will evaluate to 40 Assignment Compatibilities In an assignment statement, you can assign a value of one type into another type: int iVariable = 6; double dblVariable; dblVariable = iVariable; // assigning int to double Assignment Compatibilities However, you can not directly assign a double into an int double dblVariable = 6.75; int iVariable; iVariable = dblVariable; // assigning double to int Compiler error! Possible loss of precision Type Casting Generally, you can only assign a type to the type appearing further down the list: byte > short > int > long > float > double However, if you wish to change a double type to an int, you must use type casting Type Casting: Example double dblVariable = 6.75; int iVariable; iVariable = (int) dblVariable; // assigning double to int by typecasting The value of iVariable is now 6 The value of dblVariable is truncated and assigned to iVariable. The value of dblVariable remains 6.75 Sample Program Let's have a look at the following program. What does it do? public class SimpleMaths { public static void main (String[] args) { int num1 = 5, num2 = 6; int sum, diff, product, quotient, remainder; sum = num1 + num2; diff = num1 - num2; product = num1 * num2; quotient = num1 / num2; remainder = num1 % num2; } } Displaying output We must use display the results obtained public class SimpleMaths { public static void main (String[] args) { int num1 = 5, num2 = 6; int sum, diff, product, quotient, remainder; sum = num1 + num2; diff = num1 - num2; … System.out.println(sum); displays the System.out.println(diff); value stored in // etc the variable } sum } Displaying output However, we should always make our output meaningful and clear. public class SimpleMaths { public static void main (String[] args) { int num1 = 5, num2 = 6; int sum, diff, product, quotient, remainder; sum = num1 + num2; … System.out.println("The sum is"); System.out.println(sum); // etc } } Displaying output We can use the System.out.print() method: public class SimpleMaths { public static void main (String [] args) { int num1 = 5, num2 = 6; int sum, diff, product, quotient, remainder; sum = num1 + num2; … System.out.print("The sum is "); System.out.println(sum); // etc } } Displaying output We can combine Strings and data using the concatenation operator + public class SimpleMaths { public static void main (String [] args) { int num1 = 5, num2 = 6; int sum, diff, product, quotient, remainder; sum = num1 + num2; … System.out.print("The sum is " + sum); // etc } } Concatenation + The symbol '+' has two meanings in Java Addition plus, which adds two numbers Concatenation plus, which joins Strings or text together. Concatenation + '+' will be used for addition if: both operands are numeric System.out.println(8 + 6); System.out.println(17.5 + 4); '+' will be used to concatenate if: if either operand is a String or text System.out.println("8" + 6); System.out.println(8 + "6”) System.out.println("8" + "6”) System.out.println("The answer is " + 14); System.out.println("The answer is " + 8 + 6); Exercise Write a Java program that sets the values of three integer-valued assignment scores and then calculates and displays: the total of the three scores the average of the three scores Exercise What is wrong with the following program? public class countAvg { public static void main (String[] args) { int score1, score2; double average = 0.0; score1 = 56; score2 = 73; average = score1 + score2 / 2 System.out.print("The average of "); System.out.print(score1); System.out.print("and"); System.out.println(score2); System.out.println("is " + average); } } The Char data type Another primitive data type is char The char data type can hold values of the following character literals: the letters of the alphabet, eg.: 'A', 'b' the digits, eg. : '0' , '3' other special symbols, eg.: '(', '&', '+' the null (empty) character: '' The Char data type Invalid character literals: "a" – this is a string 'aB' – these are two characters ''' – three consecutive single quotes: what does it mean? Escape Sequence Sometimes it is necessary to represent symbols: which already have special meanings in the Java language, such as ' or " other characters such as a tab or return. Escape Sequence The escape sequence character \ is used in this case. '\'' to represent the single quote character '\"' to represent the double quote character '\\' to represent a backslash character. '\t' to represent a tab '\n' to create a new line Exercise Write a program that will display the following: She said "Hello!" to me! The String Data Type A String type is an example of a reference data type. A string is defined as a sequence of characters. The String Data Type Examples of String literals: " " (space, not the character ' ') "" (empty String) "a" "HELLO" "This is a String" "\tThis is also a String\n" Declaring a String Strings can be used to store names, titles, etc. We can declare a String data type by giving it a variable name: String name; We can also initialize the variable upon declaration: String subjectCode = “BIT106”; Exercise Write a program to print out the following, using String variables: Subject code: BIT106 Subject name: Java Programming Student name: Lee Ah Yew Assignment 1 Score (out of 25): 24.0 Assignment 2 Score (out of 25): 23.5 Exam Raw Score (out of 50) : 48.90 Lee Ah Yew's Total Score for BIT106 (Java Programming): 96.40 Keyboard Input Java 5.0 has reasonable facilities for handling keyboard input. These facilities are provided by the Scanner class in the java.util package. A package is a library of classes. Using the Scanner Class Near the beginning of your program, insert import java.util.* Create an object of the Scanner class Scanner sc = new Scanner (System.in) Read data (an int or a double, for example) int n1 = sc.nextInt(); double d1 = sc.nextDouble(); Keyboard Input Demonstration class ScannerDemo Some Scanner Class Methods syntax Int_Variable = Object_Name.nextInt(); Double_Variable = Object_Name.nextDouble(); String_Variable = Object_Name.next(); String_Variable = Object_Name.nextLine(); Remember to prompt the user for input, e.g. System.out.print(“Enter an integer: “); Interactive Input You should always prompt the user when obtaining data: Please enter your name: Sandy Lim Please enter your age: 25 Please enter your score: 87.9 Please enter your grade: A Exercise Write a program that asks the user to enter the name of an item, the price and the quantity purchased. The program must calculate the total price and display the following: Item widget Unit RM5.30 Qty 10 Total RM53.00 Pseudocode When we want to write a computer program, we should always: Think Plan Code We can write out our planning using pseudocode – writing out the steps in simple English and not strict programming language syntax. Documentation A computer programmer generally spends more time reading and modifying programs than writing new ones. It is therefore important that your programs are documented: clearly neatly meaningfully Documentation You should always precede your program with: Your name The date The purpose of the program Comments Comments are used to: Insert documentation Clarify parts of code which may be complex. Comments are ignored by the compiler but are useful to humans. Comments The symbols // are used to indicate that the rest of a line are comments. If comments span more than one line, the symbols /* and */ can be used, eg.: /* this is the beginning of the documented comments and it only ends here */ Variable names Variable names shoud: follow the Java rules be meaningful For example, name, score, totalBeforeTaxes You should almost never use names like a, b, c Variable names By convention: variable names start with a lowercase letter class names start with an uppercase letter, eg. String, Scanner Indentation Programs are also indented for clarity Indentation shows the levels of nesting for the program. public class CalcCircle { public static void main(String[] args) { int radius; // radius - variable final double PI = 3.14159; // PI - constants radius = 10; double area = PI * radius * radius; double circumference = 2 * PI * radius; } } Exercise Write a program that asks the user for their name and the year they were born. Then display their age this year. What is your name? Kelly What is your year of birth? 1982 Wow, Kelly, this year you will be 21 years old! Exercise Write a program that asks the user to enter the length and width of a rectangle and then display: the area of the rectangle the perimeter of the rectangle The Math class: We can use pre-defined methods from the Math class to perform calculations. Exercise Write a Java program that asks the user to enter two numbers, then: find the absolute value of each of the numbers; determine which absolute value is larger find the square root of the larger of the two absolute values Sample run: Enter first number: -36 Enter second number: 5 The absolute values of the two numbers are 36 and 5 The larger absolute value is 36 The square root of 36 is 6.0 Catch-up Exercise Write a Java program that asks the user to enter a double number. Then display: the square root of the number. Now test the program with the values: 39.4 -30 We want to be able to make sure that the user cannot enter negative values! Tugas Rumah NPM Ganjil Buat program untuk menghitung volume balok. NPM Genap Buat program untuk menghitung volume bola. Input data dilakukan oleh user! Bukan programmer! Gunakan class Scanner. Buat flowchart-nya terlebih dulu. Dikumpulkan maks. Jumat 1/10/2010 pukul 24.00 WIB. Di kertas atau kirim lewat email bluejundi@yahoo.com.