Review Java

1. Review Java

2. Objectives • To understand the essentials of object-oriented programming in Java • To review the primitive data types of Java, how to use the control structures of Java • To learn how to use predefined classes such as Math, JOptionPane, String, StringBuffer, and StringTokenizer • To review how to write and document your own Java classes Appendix A: Introduction to Java

3. Chapter Objectives (continued) • To understand how to use arrays in Java • To learn how to perform I/O in Java using simple dialog windows • To learn how to perform I/O in Java using streams Appendix A: Introduction to Java

4. Compiling and Executing a Java Program Appendix A: Introduction to Java

5. Classes and Objects • The class is the fundamental programming unit • Every program is written as a collection of classes • Class definitions are stored in separate files with the extension .java and the file name must be the same as the class name • A class is a named description for a group of entities • A class is a general description of a group of entities that all have the same characteristics; each entity is an object Appendix A: Introduction to Java

6. The Java API • Java consists of small core language augmented by an extensive collection of packages • Each package contains a collection of related Java classes, such as: • Swing • AWT • util Appendix A: Introduction to Java

7. Import Statements Class Comment Class Name class { Data Members Methods (incl. Constructor) } Review of Java fundamentals Template for Class Definition

8. Primitive Data Types and Reference Variables • Java distinguishes two kinds of entities • Primitive types: data is stored in primitive type variables • Objects: are associated with reference variables which store an object’s address Appendix A: Introduction to Java

9. Primitive Data Types • Represent numbers, characters, and Boolean values • Integers: byte, short, int, and long • Real numbers: float and double • Characters: char Appendix A: Introduction to Java

10. 9 For example, character 'O' is 79 (row value 70 + col value 9 = 79). O 70 ASCII Encoding

11. Variable declaration Format: <data type> <variable_name>; If more than one variable has the same data type: <data type> <name1>, <name2>..;

12. Assignment statement <variable name> = <expression>; Example: x =2*5+6-1;

13. Variable names • It must be a legal identifier. • It must not be a keyword, a boolean literal (true or false), or the reserved word null. • It must be unique within its scope.

14. Variable name (cont.) • Legal identifier:be composed of letters, numbers, _ and $. Identifiers may only begin with a letter, _, or $. • Keyword: http://java.sun.com/docs/books/tutorial/java/nutsandbolts/_keywords.html • Java styles: • Variablenames begin with a lowercase letter • Class names begin with an uppercase letter

15. Review question Which of the following is not a valid Java identifier? a. myValue b. $_AAA1 c. width d. m_x Appendix A: Introduction to Java

16. Review question Which of the following is not a valid Java identifier? a. myValue b. $_AAA1 c. width d. m_x Appendix A: Introduction to Java

17. Review question Which of the following is a correct variable declaration statement? a. int x - float y; b. int x: float y; c. intx,y; d. Long int x; Appendix A: Introduction to Java

18. Review question Which of the following is a correct variable declaration statement? a. int x - float y; b. int x: float y; c. intx,y; d. Long int x; Appendix A: Introduction to Java

19. Constant and variables • Constant: • Value it contains doesn’t change final int MONTHS_IN_YEAR = 12; • Variables: • Value it contains may vary double loanAmount; • loanAmount =0; • loanAmount = 1000.99;

20. Integer division and type casting • Integer division: • Integer/integer = integer, 7/2 = 3 • Integer/double = double, 7/2.0 = 3.5 • Double/integer = double, 7.0/2 = 3.5 • Type casting: a process that converts a value of one data type to another data type.Implicit casting Explicit casting

21. Type casting (cont.) • Implicit casting: • Operand is converted from a lower to a higher precision • Higher precision: a data type with a larger range of values • Double has a higher precision than float • Int has a higher precision than short • Operand: can be a constant, variable, method call or another arithmetic expression

22. Type casting (cont.) • Explicit casting • (<data type>) <expression> • Example: float result; result = (float) ((3+5)/6); and result = ((float) (5+3))/6;

23. Type Compatibility and Conversion • Widening conversion: operations involving mixed-type operands, the numeric type of the smaller range is converted to the numeric type of the larger range • In an assignment operation, a numeric type of smaller range can be assigned to a numeric type of larger range Appendix A: Introduction to Java

24. Control Statements: Simple Choice Statement if (<boolean expression>) <block>; else <block>; if (<boolean expression>) single statement; else single statement;

25. Boolean expression • Boolean expression: is a conditional expression that is evaluated to either true or false. • Conditional expression: is a three part expression: <exp.> <relational operators> <exp.> • Boolean expressions can be combined by boolean operators

26. Relational Operators

27. Boolean operators && means AND || means OR ! means NOT

28. Pre-review question • How many times the method readData() will be called in the following code segnment? inti;i = 0; while ( i <= 4 ) { readData(); i = i + 1; } // end while 5 Appendix A: Introduction to Java

29. Pre-review question . can be used to traverse a two-dimensional array. a. A do while statement. b. A for statement. c. Two nested for statements. d. Three nested for statements. Appendix A: Introduction to Java

30. Pre-review question . can be used to traverse a two-dimensional array. a. A do while statement. b. A for statement. c. Two nested for statements. d. Three nested for statements. Appendix A: Introduction to Java

31. The While Loop while(<boolean expression>){ // Repeat multiple statements. statement 1 statement 2 statement 3 ... }

32. The Do-While Loop do { // Repeat multiple statements. statement 1 statement 2 statement 3 ... } while(<boolean expression); • Note that the statements in the body of the loop are always executed at least one. • Note the final semicolon, which is required.

33. The For-Loop Outline // Repeat multiple statements. for(initialization; condition; post-body update){ // Statements to be repeated. statement 1 statement 2 statement 3 ... } • Commonly used with increment • and decrement operators.

34. Increment and Decrement • Used as a shorthand for add-one-to and subtract-one-from: • value = value+1; • value += 1; • value++; • Prefix and postfix forms: • ++value; • --value; • value--;

35. <modifiers> <data type> <name> ; Attributes (Data Member) Declaration Modifiers Data Type Name • private String ownerName ; Note: There’s only one modifier in this example.

36. <modifier> <return type> <method name> ( <parameters> ){ • <statements> • } Method Declaration Modifier Return Type Method Name Parameter • public void setOwnerName ( String name ){ • ownerName = name; • } Statements

37. public <class name> ( <parameters> ){ <statements> } Constructor • A constructor is a special method that is executed when a new instance of the class is created. Modifier Class Name Parameter • public Bicycle ( ) { • ownerName = “Unassigned”; • } Statements

38. argument Arguments and Parameters • An argument is a value we pass to a method. • A parameter is a placeholder in the called method to hold the value of the passed argument. class Sample { public static void main(String[] arg) { Account acct = new Account(); . . . acct.add(400); . . . } . . . } class Account { . . . public void add(double amt) { balance = balance + amt; } . . . }

39. Arguments and Parameters • An argument is a value we pass to a method. • A parameter is a placeholder in the called method to hold the value of the passed argument. class Sample { public static void main(String[] arg) { Account acct = new Account(); . . . acct.add(400); . . . } . . . } class Account { . . . public void add(double amt) { balance = balance + amt; } . . . } parameter

40. Referencing and Creating Objects • You can declare reference variables that reference objects of specified types • Two reference variables can reference the same object • The new operator creates an instance of a class • A constructor executes when a new object is created Appendix A: Introduction to Java

41. Methods • Programmers use methods to define a group of statements that perform a particular operation • The modifier static indicates a static or class method • A method that is not static is an instance method • All method arguments are call-by-value • If the argument is a primitive type, its value is passed to the method • The method can’t modify the argument value and have the modification remain after return from the method Appendix A: Introduction to Java

42. Methods (continued) • If the argument is of a class type, the value of the reference variable is passed, not the value of the object itself • Reference variables point to the object and any modification to the object will remain after return from the method Appendix A: Introduction to Java

43. Review question Consider the following Java statements: int x = 9; double y = 5.3; result = calculateValue( x, y ); Which of the following statements is false? a. A method is called with its name and arguments inside parentheses. b. x and y are parameters. c. Copies of x and y are passed to the method calculateValue(). d. x and y are arguments Appendix A: Introduction to Java

44. Review question Consider the following Java statements: int x = 9; double y = 5.3; result = calculateValue( x, y ); Which of the following statements is false? a. A method is called with its name and arguments inside parentheses. b. x and y are parameters. c. Copies of x and y are passed to the method calculateValue(). d. x and y are arguments Appendix A: Introduction to Java

45. The Class Math • Provides a collection of methods that are useful for performing common mathematical operations Appendix A: Introduction to Java

46. Escape Sequences • An escape sequence is a sequence of two characters beginning with the character \ • Represents characters or symbols that have a special meaning in Java Appendix A: Introduction to Java

47. The String Class • String class defines a data type that is used to store a sequence of characters • You cannot modify a String object • If you attempt to do so, Java will create a new object that contains the modified character sequence Appendix A: Introduction to Java

48. Comparing Objects • You can’t use the relational operators or equality operators to compare the values stored in strings or other objects Appendix A: Introduction to Java

49. Examples We can do this because String objects are immutable.

50. The StringBuffer Class • Stores character sequences • Unlike a String object, the contents of a StringBuffer object can be changed