Spring 09- ICE0124 Programming Fundamentals I Java Programming

1. Spring 09- ICE0124 Programming Fundamentals IJava Programming XuanTung Hoang tung_hx@icu.ac.kr Lecture No. 2

2. Introduction to Java Programming and Applications Compiler/Interpreter Java language Java Platforms, JRE and JDK First programs: Hello world, and Addition Syntax: Things to remember … … Other experiences Memory concepts Primitive Data Types Expression, Arithmetic and relation operators

3. Interpreter and Complier • Computers need translators to translate high-level language to machine instructions • Interpreter translates programs (written in high-level languages) online: • Translate and execute at the same time • Statement by statement • Compiler translates the whole program into machine language before execution • Turn program’s text into executable file (in machine language format) • When user wants to run the program, he/she loads the executable file into computer memory to execute. • Portability issue: Different computer hardwares use different instruction sets (machine language) • We need appropriate interpreter/compiler for each type of machine

4. History of Java language • Initially, Java language is developed for consumer-electronic devices (embedded systems) (in 1991 by Sun Microsystems) • Also, It turned out to be good for Web and Internet applications • Add dynamic contents (Java applet) • Rapid development of distributed applications • Ease of deployment • … now Java becomes more and more attractive for embedded systems (its primary purpose)

5. Java Platforms • Sun Microsystems provides most of the utilities for users in “Java Platform” products • Text editor • Bytecode compiler • Class loader • Bytecode Verifier • JVM (interpreter) • … Plain text editor: GVIM, Crimson editor, Ultraedit, … Rich text editor: MSWord,… Java Platforms: J2SE, J2EE, J2ME

6. Java Platforms • J2SE: Standard Edition • J2EE: Enterprise Edition • J2ME: Micro Edition • JDK v.s. JRE + bytecode compiler + Class libraries + … JDK + JVM (interpreter) + … JRE

7. Java Development Process • 5 phases • Creating a program: use text editor to create program source • Compiling: use compiler to turn program source into bytecode (.class files) • Loading: use class loader to load .class files into memory • Bytecode verification: bytecode verifier examines the bytecode for validity and security concerns • Execution: Java Virtual Machine (is a kind of interpreter for bytecodes) executes the bytecodes • Combination of compiling and interpreting • Enhance portability of programs: • Write Once – Run Anywhere • Compact bytecode files are easy to exchange • Bytecode verifier guarantees security • Just-In-Time compiler enhances performance

8. First Application

9. First Application: Structure • Hello.java defines one class: class Hello • Keyword class is used for defining a class • Class name follows keyword class • Class body is surrounded by braces { … }

10. First Application: Structure • Class body contains methods (or class functions) and variables: • In the example we have only one method (method main) and no variables • Method has return type (void) and parameters ( args ) • Parameters are given within parenthesis ( … ) • If the method have no parameters, parenthesis are still required • Modifiers public and static characterize the method • Braces surrounds method body • main method is the program entry • Every java program must have one main function

11. First Application: Structure • Inside method body, there are statements. • There is only one statement in the example. • Each statement should be ended with a semicolon “;” • One statement may span multiple lines

12. First Application: Comments • Multi-line comments with: /* … */ • Single-line comments with: // • Comments can be placed anywhere. • Comments are for human (compiler ignores comments) • Comments should explain the code

13. More complex program: Addition

14. More complex program: Addition • import statement specifies external classes that we use in our program • In the example: • Scanner is the class we use • Scanner is a class in class libraries provided by JDK

15. More complex program: Addition Variables declaration Using Scanner object to read input Do computation & display result

16. Read input and display output • Read input with Scanner class • Import Scanner class • import java.util.Scanner; • Create Scanner object • Scanner input = new Scanner( System.in ); • Read input from user using nextInt() method • number1 = input.nextInt(); • Read textbook, section 2.5 • Display input with print, println, printf • System.out.print(“abc”): output the string “abc” • System.out.println(“abc”): outputs the string “abc” then goes to the next line • System.out.printf(“result is %d”, sum): output a string with format specifiers • Read textbook section 2.4

17. Things to remember … • Java is case-sensitive: class and Class are different • Skeleton of a class • Skeleton of a class function (method) • Skeleton of a simple java program • Simple Java program has one class that contains main method • Name of the source file must be identical to the class name (class identifier) • Statements end with “;” • Braces enclose blocks of code • Braces should go in pairs (Good practice: Open and close brace together) • Read input from user and output result to screen

18. Other experiences… • Observe outputs of java compiler (javac.exe) when compiling java program (.java file) • When the compilation is successful • What files are produced by javac.exe • What is stored inside those files (files produced by javac) • When the compilation failed • Specify the problem in your source code

19. Variable and Memory • Example of variables: • A variable is associated with a location in memory • A variable has: • Name: is used to access the memory location • Type (data type): specifies how the variable is treated by the computer • Size: The size of the memory location; is determined according to type of the variable • Value: is stored in binary format at the memory location type name

20. Variable and Memory: Illustration • What does the following 16-bit string represent ? 00010100100000000 • If you don’t understand, please read textbook, section 2.6

21. Primitive data types and Objects • There are many data types • We can even define our own data type • Data types are classified into primitive data types and reference types (objects) • Primitives data types: • … are most fundamental • … use small, fixed number of bytes • … are built into Java • … are used as building block for developing more complex data types (objects) • There are 8 primitive data types: • byte, short, int, long, fload, double, char, boolean • Is Int a Java primitive data type ? Floating point numbers Logical (True/false) Integral numbers characters

22. Number data types • Number literals • Valid integers: 2007 2007L (long integer) • Valid floating point numbers: 2007, 2007.0 2007f, 2007.1f (float) 2007d, 2007.1d (double) 3.4E+3 (scientific notation) Can we use byte data type to store the number 2007 ?

23. char data type and Character table • Size of char is 2 bytes (16 bits) • Character table is used to map 16-bit codes to letters (Unicode) • Character literal: • Valid characters: ‘a’, ‘b’, ‘A’, ‘\n’, ‘\t’ Is it a character “C” ?

24. boolean data type • Accept only two values: true and false • They are Java keywords

25. Expressions and Arithmetic Expressions • Expression is a combination of literals, operators and parenthesis to produce a value • Example: • a + b * c (a, b, c are variables already declared) • Expressions dealing with number variables and operators are arithmetic expressions • Arithmetic operators in Java: + , -, *, /, % • Be careful with division operator /: • Integer division is different from floating point division • 3 / 2  1 • 3.0 / 2  1.5 • How about remainder operator with floating point numbers ?

26. Order of calculation and Precedence • Order of calculations: • Parenthesis • *, /, % • +/- • Left to right • Examples

27. Equality and Relation operators • Equality operators : ==, != • Relational operators: <, >, <=, >= • See fig 2.14, section 2.8, textbook • Questions: • Assume that we declare integer variable a and b and assign values 3 to a, and 4 to b. • Is a < b a valid expression ? • What values are produced by a < b, a < b, a == b?

28. Equality and relation operators • Be careful when using == with float/double variables • Does this produce true ? • 4.0/3.0 == 1.0 + 1.0/3.0 • How about this ? • 1.0/3.0 = 0.333333333333333 • Floating point arithmetic is NOT exact • Exact equality sometimes impossible to achieve  Logically we expect true but the computer report false • Avoid using equality with floating point numbers

29. Two’s complement notation(Appendix E6, textbook) • Assume 4-bit signed integers • Arithmetic negation "-" is equivalent to "~" then + 1

30. Floating-point number precision • Two data type (primitive) for floating point numbers: float and double • float: 32-bit (4-byte). Ex: 0.12f • double: 64-bit (8-byte). Ex: 4.15d • Floating-point numbers are treated as double by default • Example: 9.02 and 9.02d are all double numbers • Floating-point number arithmetic are approximate

31. Assignment • Assignment operator, = • Stores the value evaluated on “the right hand side” into the variable on “the left hand side” • Example: