Chapter 2 Primitive Data Types and Operations.ppt

1、Chapter 2 Primitive Data Types and Operations,Introduce Programming with an Example Identifiers, Variables, and Constants Primitive Data Types byte, short, int, long, float, double, char, boolean Expressions Operators, Precedence, Associativity, Operand Evaluation Order: +, -, *, /, %, +=, -=, *=, /

2、=, %=, , &, |, +, -, Getting Input from Input Dialog Boxes Case Studies (Computing Mortgage, and Computing Changes) Style and Documentation Guidelines Syntax Errors, Runtime Errors, and Logic Errors,Introducing Programming with an Example,Example 2.1 Computing the Area of a CircleThis program comput

3、es the area of the circle.,ComputeArea,Run,Identifiers,An identifier is a sequence of characters that consist of letters, digits, underscores (_), and dollar signs ($). An identifier must start with a letter, an underscore (_), or a dollar sign ($). It cannot start with a digit. An identifier cannot

4、 be a reserved word. (See Appendix A, “Java Keywords,” for a list of reserved words). An identifier cannot be true, false, or null. An identifier can be of any length.,Variables,/ Compute the first area radius = 1.0; area = radius*radius*3.14159; System.out.println(“The area is “ + area + “ for radi

5、us “+radius);/ Compute the second area radius = 2.0; area = radius*radius*3.14159; System.out.println(“The area is “ + area + “ for radius “+radius);,Declaring Variables,int x; / Declare x to be an/ integer variable; double radius; / Declare radius to/ be a double variable; char a; / Declare a to be

6、 a/ character variable;,Assignment Statements,x = 1; / Assign 1 to x; radius = 1.0; / Assign 1.0 to radius; a = A; / Assign A to a;,Declaring and Initializing in One Step,int x = 1; double d = 1.4; float f = 1.4;Is this statement correct?,Constants,final datatype CONSTANTNAME = VALUE; final double P

7、I = 3.14159; final int SIZE = 3;,Numerical Data Types,byte 8 bits short 16 bits int 32 bits long 64 bits float 32 bits double 64 bits,Operators,+, -, *, /, and %5/2 yields an integer 2. 5.0/2 yields a double value 2.55 % 2 yields 1 (the remainder of the division),NOTE,Calculations involving floating

8、-point numbers are approximated because these numbers are not stored with complete accuracy. For example, System.out.println(1 - 0.1 - 0.1 - 0.1 - 0.1 - 0.1); displays 0.5000000000000001, not 0.5, and System.out.println(1.0 - 0.9); displays 0.09999999999999998, not 0.1. Integers are stored precisely

9、. Therefore, calculations with integers yield a precise integer result.,Number Literals,A literal is a constant value that appears directly in the program. For example, 34, 1,000,000, and 5.0 are literals in the following statements:int i = 34; long l = 1000000; double d = 5.0;,Integer Literals,An i

10、nteger literal can be assigned to an integer variable as long as it can fit into the variable. A compilation error would occur if the literal were too large for the variable to hold. For example, the statement byte b = 1000 would cause a compilation error, because 1000 cannot be stored in a variable

11、 of the byte type. An integer literal is assumed to be of the int type, whose value is between -231 (-2147483648) to 2311 (2147483647). To denote an integer literal of the long type, append it with the letter L or l. L is preferred because l (lowercase L) can easily be confused with 1 (the digit one

12、).,Floating-Point Literals,Floating-point literals are written with a decimal point. By default, a floating-point literal is treated as a double type value. For example, 5.0 is considered a double value, not a float value. You can make a number a float by appending the letter f or F, and make a numb

13、er a double by appending the letter d or D. For example, you can use 100.2f or 100.2F for a float number, and 100.2d or 100.2D for a double number.,Scientific Notation,Floating-point literals can also be specified in scientific notation, for example, 1.23456e+2, same as 1.23456e2, is equivalent to 1

14、23.456, and 1.23456e-2 is equivalent to 0.0123456. E (or e) represents an exponent and it can be either in lowercase or uppercase.,Arithmetic Expressions,is translated to(3+4*x)/5 10*(y-5)*(a+b+c)/x + 9*(4/x + (9+x)/y),Shortcut Assignment Operators,Operator Example Equivalent += i+=8 i = i+8 -= f-=8

15、.0 f = f-8.0 *= i*=8 i = i*8 /= i/=8 i = i/8 %= i%=8 i = i%8,Increment and Decrement Operators,Increment and Decrement Operators, cont.,Increment and Decrement Operators, cont.,Using increment and decrement operators makes expressions short, but it also makes them complex and difficult to read. Avoi

16、d using these operators in expressions that modify multiple variables, or the same variable for multiple times such as this: int k = +i + i.,Assignment Expressions and Assignment Statements,Prior to Java 2, all the expressions can be used as statements. Since Java 2, only the following types of expr

17、essions can be statements: variable op= expression; / Where op is +, -, *, /, or % +variable; variable+; -variable; variable-;,Numeric Type Conversion,Consider the following statements: byte i = 100; long k = i*3+4; double d = i*3.1+k/2;int x = k; /(Wrong) long k = x; /(fine,implicit casting),Type C

18、asting,double float long int short byte,Type Casting, cont.,Implicit castingdouble d = 3; (type widening)Explicit castingint i = (int)3.0; (type narrowing)What is wrong? int x = 5/2.0;,Character Data Type,char letter = A; (ASCII) char numChar = 4; (ASCII) char letter = u0041; (Unicode) char numChar

19、= u0034; (Unicode)Special characters char tab = t;,Unicode Format,Description Escape Sequence Unicode Backspace b u0008 Tab t u0009 Linefeed n u000a Carriage return r u000d,Appendix B: ASCII Character Set,ASCII Character Set is a subset of the Unicode from u0000 to u007f,ASCII Character Set, cont.,A

20、SCII Character Set is a subset of the Unicode from u0000 to u007f,Casting between char and Numeric Types,int i = a; / Same as int i = (int)a;char c = 97; / Same as char c = (char)97;,The boolean Type and Operators,boolean lightsOn = true; boolean lightsOn = false; boolean b = (1 2); & (and) (1 x) &

21、(x 100) | (or) (lightsOn) | (isDayTime) ! (not) !(isStopped),Comparison Operators,Operator Name greater than = greater than or equal to = equal to != not equal to,Boolean Operators,Operator Name ! not & and | or exclusive or,Truth Table for Operator !,Truth Table for Operator !Operand !Operand true

22、false false true,Truth Table for Operator &,Operand1 Operand2 Operand1 & Operand2 false false false false true false true false false true true true,Truth Table for Operator |,Operand1 Operand2 Operand1 | Operand2 false false false false true true true false true true true true,Truth Table for Opera

23、tor ,Operand1 Operand2 Operand1 Operand2 false false false false true true true false true true true false,The & and | Operators,&: conditional AND operator &: unconditional AND operator |: conditional OR operator |: unconditional OR operatorexp1 & exp2 (1 x) & (x 100)(1 x) & (x 100),The & and | Ope

24、rators,If x is 1, what is x after this expression? (x 1) & (x+ x) & ( 1 x+)How about (1 = x) | (10 x+)? (1 = x) | (10 x+)?,Operator Precedence,How to evaluate3 + 4 * 4 5 * (4 + 3) - +i,Operator Precedence,var+, var- +, - (Unary plus and minus), +var,-var (type) Casting ! (Not) *, /, % (Multiplicatio

25、n, division, and modulus) +, - (Binary addition and subtraction) , = (Comparison) =, !=; (Equality) & (Unconditional AND) (Exclusive OR) | (Unconditional OR) & (Conditional AND) Short-circuit AND | (Conditional OR) Short-circuit OR =, +=, -=, *=, /=, %= (Assignment operator),Operator Associativity,W

26、hen two operators with the same precedence are evaluated, the associativity of the operators determines the order of evaluation. All binary operators except assignment operators are left-associative.a b + c d is equivalent to (a b) + c) d Assignment operators are right-associative. Therefore, the ex

27、pressiona = b += c = 5 is equivalent to a = (b += (c = 5),Operand Evaluation Order,The precedence and associativity rules specify the order of the operators, but do not specify the order in which the operands of a binary operator are evaluated. Operands are evaluated from left to right in Java. The

28、left-hand operand of a binary operator is evaluated before any part of the right-hand operand is evaluated.,Operand Evaluation Order, cont.,If no operands have side effects that change the value of a variable, the order of operand evaluation is irrelevant. Interesting cases arise when operands do ha

29、ve a side effect. For example, x becomes 1 in the following code, because a is evaluated to 0 before +a is evaluated to 1. int a = 0; int x = a + (+a); But x becomes 2 in the following code, because +a is evaluated to 1, then a is evaluated to 1. int a = 0; int x = +a + a;,Getting Input from Input D

30、ialog Boxes,String string = JOptionPane.showInputDialog(null, “Prompt Message”, “Dialog Title”, JOptionPane.QUESTION_MESSAGE); where x is a string for the prompting message and y is a string for the title of the input dialog box.,Convertting Strings to Integers,The input returned from the input dial

31、og box is a string. If you enter a numeric value such as 123, it returns “123”. To obtain the input as a number, you have to convert a string into a number. To convert a string into an int value, you can use the static parseInt method in the Integer class as follows:int intValue = Integer.parseInt(i

32、ntString);where intString is a numeric string such as “123”.,Convertting Strings to Doubles,To convert a string into a double value, you can use the static parseDouble method in the Double class as follows:double doubleValue =Double.parseDouble(doubleString);where doubleString is a numeric string su

33、ch as “123.45”.,Example 2.2 Entering Input from Dialog Boxes,InputDialogDemo,Run,This program first prompts the user to enter a year as an int value and checks if it is a leap year, it then prompts you to enter a double value and checks if it is positive. A year is a leap year if it is divisible by

34、4 but not by 100, or it is divisible by 400.,Example 2.3 Computing Mortgages,ComputeMortgage,Run,This program lets the user enter the interest rate, number of years, and loan amount and computes monthly payment and total payment.,Example 2.4 Computing Changes,This program lets the user enter the amo

35、unt in decimal representing dollars and cents and output a report listing the monetary equivalent in single dollars, quarters, dimes, nickels, and pennies. Your program should report maximum number of dollars, then the maximum number of quarters, and so on, in this order.,ComputeChange,Run,Programmi

36、ng Style and Documentation,Appropriate Comments Naming Conventions Proper Indentation and Spacing Lines Block Styles,Appropriate Comments,Include a summary at the beginning of the program to explain what the program does, its key features, its supporting data structures, and any unique techniques it

37、 uses. Include your name, class section, instruction, date, and a brief description at the beginning of the program.,Naming Conventions,Choose meaningful and descriptive names. Variables and method names: Use lowercase. If the name consists of several words, concatenate all in one, use lowercase for

38、 the first word, and capitalize the first letter of each subsequent word in the name. For example, the variables radius and area, and the method computeArea.,Naming Conventions, cont.,Class names: Capitalize the first letter of each word in the name. For example, the class name ComputeArea.Constants

39、: Capitalize all letters in constants. For example, the constant PI.,Proper Indentation and Spacing,Indentation Indent two spaces.Spacing Use blank line to separate segments of the code.,Block Styles,Use end-of-line style for braces.,Programming Errors,Syntax Errors Detected by the compiler Runtime

40、Errors Causes the program to abort Logic Errors Produces incorrect result,Compilation Errors,public class ShowSyntaxErrors public static void main(String args) i = 30;System.out.println(i+4); ,Runtime Errors,public class ShowRuntimeErrors public static void main(String args) int i = 1 / 0; ,Logic Er

41、rors,public class ShowLogicErrors / Determine if a number is between 1 and 100 inclusivelypublic static void main(String args) / Prompt the user to enter a numberString input = JOptionPane.showInputDialog(null, “Please enter an integer:“,“ShowLogicErrors“, JOptionPane.QUESTION_MESSAGE);int number = Integer.parseInt(input);/ Display the resultSystem.out.println(“The number is between 1 and 100, “ + “inclusively? “ + (1 number) ,