2. General Features of Java Programming Language Variables and Data Types Operators Expressions Control Flow Statements

3. The Basic Demo Program public class BasicsDemo { public static void main(String[] args) { int sum = 0; for (int current = 1; current <= 10; current++) { sum += current; } System.out.println("Sum = " + sum); }

4. The Count Class import java.io.*; public class Count { public static void countChars(Reader in) throws IOException { int count = 0; while (in.read() != -1) count++; System.out.println("Counted " + count + " chars."); } } Go Back: 6, 8, 176817

5. Running the countChars import java.io.*; public class Count { //... countChars method omitted... public static void main(String[] args) throws Exception { if (args.length >= 1) countChars(new FileReader(args[0])); else System.err.println("Usage: Count filename"); } }

6. Variables and Data Types Variables: Entities that act or are acted upon Two Variables in Count: count and in

7. Variable Declaration Variable Declaration: –Type of the variable –Name of the variable The location of the variable declaration determines its scope.

8. Data Type Java is static-typed: All variables must have a type and have to be declared before use. A variable's data type determines its value and operation Two categories of data types in Java –primitive data type: byte, short, int, long, float....primitive data type –reference data type: class, interface, array count is ? in is ? Primitive Reference

9. Primitive and Reference Data Type int x; x = 5; x: 5 Point p1, p2; p1 = new Point(); p2 = p1; p1:p2: x: 0 y: 0 Primitive Data Type Reference Data Type

10. Primitive Data Types byte 8-bit short16-bit int32-bit long64-bit float32-bit floating point double64-bit floating point char16-bit Unicode booleantrue/false

11. Variable Names Java refers to a variable's value by its name. General Rule –Must be Legal Java identifier –Must not be a keyword or a boolean literal –Must not be the same name as another variable in the same scope Convention: –Variable names begin with a lowercase letter isEmpty, isVisible, count, in –Class names begin with an uppercase letter Count

12. Reserved Words (Keywords) abstract default if private throw boolean do implementsprotectedthrows break double importpublic transient byte else instanceofreturn try case extends int short void catch final interfacestatic volatile char finally long super while class float native switch const* for new synchronized continue goto* packagethis Don't worry about what all these words mean or do, but be aware that you cannot use them for other purposes like variable names.

13. Variable Scope The block of code within which the variable is accessible and determines when the variable is created and destroyed. The location of the variable declaration within your program establishes its scope Variable Scope: –Member variable –Local variable –Method parameter –Exception-handler parameter

14. Variable Scope

15. Variable Initialization Local variables and member variables –can be initialized with an assignment statement when they're declared. –The data type of both sides of the assignment statement must match. int count = 0; Method parameters and exception-handler parameters – cannot be initialized in the same way as local/member vars –The value for a parameter is set by the caller.

16. Final Variables The value of a final variable cannot change after it has been initialized. You can view final variables as constants. Declaration and Initialization –final int aFinalVar = 0; –final int blankfinal;... blankfinal = 0;

17. Literals (I) To represent the primitive types Integer –Decimal Value –Hexadecimal Value: 0x...(0x1f = 31) –Octal Value: 0...(076=62) Floating Point –3.1415 –6.1D2(64-bit Double; Default) –3.4F3(32-bit Float)

18. Literals (II) Characters –'..... ‘ e.g. ‘a’ –'\t', '\n'(Escape Sequence) Strings –".......“ e.g. “Hello World!” –String Class (Not based on a primitive data type)

19. Operators Operators perform some function on operands. An operator also returns a value.

20. Operators (I) Arithmetic Operators –Binary: +, -, *, /, % –Unary: +, -, op++, ++op, op--, --op Relational Operators –>, >=, <, <=, ==, !=(return true and false) Conditional Operators –&&(AND), ||(OR), !(NOT), &(AND), |(OR) –expression ? op1 : op2 Bitwise Operators –>>, >>, &, |,^,~ (i>5) ? j=1 : j=2 if (i>5) j=1; else j=2;

21. Operators (II) Assignment Operators –= –+= –-=, *=, /=, %=, &=, !=, ^=, >=, >>>= op1 += op2 s += 2 op1 = op1 + op2 s = s + 2

22. Expressions Perform the work of a Java Program Perform the computation Return the result of the computation

23. Expression An expression is a series of variables, operators, and method calls that evaluates to a single value. –count ++ –in.read() != -1 Precedence –Precedence TablePrecedence Table –Use (.....) Equal precedence –Assignment: Right to Left(a = b =c) –Other Binary Operators: Left to Right

24. Expressions and operators An expression is a program fragment that evaluates to a single value –double d = v + 9 * getSalary() % PI; Arithmetic operators –additive +, -, ++, -- –multiplicative *, / % (mod operator) Relational operators –equality == (NB) –inequality != –greater than and less than >, >=, <, <=

25. Control Flow Statement

26. If Statements if (boolean) { /*... */} else if (boolean) { /*... */} else { /*... */} The expression in the test must return a boolean value –Zero('') can't be used to mean false, or non-zero("...") to mean true Statement Block

27. Example if (income < 20000){ System.out.println (“poor”); } else if (income < 40000){ System.out.println (“not so poor”); } else if (income < 60000){ System.out.println (“rich”); } else { System.out.println (“ very rich”); }

28. Loops while (boolean expression) { /*... */ } do { /*... */ } while (boolean expression) for (expression; booleanExpression; expression) { /*... */ }

29. Example // count from 1 to 10 int i = 1; while (i<=10) { System.out.println (i); i= i+ 1; }

30. Example // count from 1 to 10 int i = 1; do { System.out.println (i) i= i+ 1; } while (i< 10);

31. The for statement The for statement has the following syntax: for (initialisation; condition; increment) statement; Reserved word The initialisation part is executed once before the loop begins The statement is executed until the condition becomes false The increment part is executed at the end of each iteration

32. Example // count from 1 to 10 for (int i = 0; i < 10; i++) System.out.println (i);

33. Secret! A for Loop can always be converted to a while loop i = 0; while (i < 10) { System.out.println(i);i++; } i++ for(i = 0; i < 10; i++) { System.out.println(i); } This will help you understand the sequence of operations of a for loop

34. Switch switch (expression) { case Constant1: /*... */ break; case Constant2: /*... */ break;.... default: /*... */ break; }

35. Multiple Selections via switch Note the "optional" default case at the end of the switch statement. It is technically optional only in terms of syntax. switch (number) { case 1: System.out.println ("One"); break; case 2: System.out.println ("Two"); break; case 3: System.out.println ("Three"); break; default: System.out.println("Not 1, 2, or 3"); break; // Needed??? } // switch For safety and good programming practice, always include a 'default' case. This might work without the default case, but would be poor technique

36. How many days? if (month == 4 || month == 6 || month == 9 || month == 11) numdays = 30; else if (month == 2) { numdays = 28; if (leap) numdays = 29; } else numdays = 31;

37. Switch switch (month) { case 4: case 6: case 9: case 11: numdays = 30; break; case 2: numdays = 28; if(leap) numdays = 29; break; default: /* Good idea? */ numdays = 31; }