Java Basics.ppt | Integer (Computer Science) | Data Type

Chapter 3

Fundamental Data Types of Java Lecture Slides to Accompany

An Introduction to Computer Science Using Java (2nd Edition) by S.N. Kamin, D. Mickunas, E. Reingold

Chapter Preview In this chapter we will: • discuss four important data types – – – –

integers real numbers strings characters

• describe the process of developing and debugging a Java program

Integers • Numbers without fractional parts 3, 47, -12 • Variables can be used to store integers using an assignment statement int daysInWeek; daysInWeek = 7;

• In general integer variables may be used any place an integer literal can be

Reading Integers import CSLib.*; Inputbox in; int i; in = newInputBox(); in.setPrompt(“Enter an integer: “); i = in.readInt();

Integer Arithmetic Operations Symbol

Operation

Example

+

Addition

45 + 5 = 50

-

Subtraction

657 – 57 = 600

*

Multiplication 7000 * 3 = 2100

/

Division

10 / 3 = 3

Remainder

10 % 3 = 1

%

Precedence Rules 1. Evaluate all subexpressions in parentheses 2. Evaluate nested parentheses from the inside out 3. In the absence of parentheses or within parentheses a. Evaluate *, /, or % before + or – b. Evaluate sequences of *, /, and % operators from left to right c. Evaluate sequences of + and – operators from left to right

Precedence Examples • Example 1 6 + 37 % 8 / 5 is the same as 6 + ((37 % 8) / 5) = 6 + ( 5 / 5) = 7

• Example 2 6 + 37 % (8 / 5) = 6 + 37 % 1 = 6+0=6

Additional Integer Operators • Self-assignment temperature = temperature + 10;

• Increment cent++; equivalent to cent = cent + 1;

• Decrement cent--; equivalent to cent = cent - 1;

Initializers • May be used to give variables initial values int x = 5; int y = 6;

• Can be written more concisely int x = 5, y = 6;

• Can use expressions on the right hand side int x = 5, y = x + 1;

Symbolic Constants • Useful when you want a variable whose value never changes • Use the modifier final in its declaration • Example final int US_Population = 278058881;

Real Numbers • Numbers with fractional parts 3.14159, 7.12, 9.0, 0.5e001, -16.3e+002 • Declared using the type double double pricePerPound = 3.99; taxRate = 0.05; shippingCost = 5.55;

• The initialization part of the declaration is optional

Real Arithmetic Operations Symbol

Operation

+

Addition

-

Subtraction

*

Multiplication

/

Division

Example 4.50e01 + 5.30e00 = 5.03e01 6.57e02 – 5.7oe01 = 6.00e02 7e02 * 3.0e00 = 2.1e04 9.6e01 / 2e01 = 4.8e00

Reading Real Numbers import CSLib.*; Inputbox in; double temp; in = newInputBox(); in.setPrompt(“Enter a real number: “); temp = in.readDouble();

Strings • String is a class defined in the java.lang package • Unlike other Java classes String has literals and a defined operation • Examples String prompt = “Enter an integer:”; String t1 = “To be “, t2 = “or not to be”; out.print(t1 + t2); Out.print(“Mass is “ + x * 2.2 + “ Kg”);

String Method Examples OutputBox out = new OutputBox(); String s1 = “Here is a test string”; out.println(s1.indexOf(“s”)); // prints 6 out.println(s1.indexOf(“x”)); // prints 1 out.println(s1.length()); 22

// prints

out.println(s1.substring(8,14)); // prints ‘a test’

Reading Strings import CSLib.*; Inputbox in; String input; in = newInputBox(); in.setPrompt(“Enter a real number: “); input = in.readString();

Characters • Any key you type on the keyboard generates a character which may or may not be displayed on the screen (e.g. nonprinting characters) • Characters are a primitive type in Java and are not equivalent to strings • Examples char vitamin = ‘’A’, chromosome = ‘’y’, middleInitial = ‘’N’;

Important Literal Characters ‘A’, … ,‘Z’ ‘a’, … ,‘z’

Uppercase letters Lowercase letters

‘0’, … , ‘9’ ‘.’,’,’,’!’,’”’,etc. ‘ ’

Digits Punctuation Marks Blank

‘\n’ ‘\t’ ‘\\’

New line Tab Backslash

‘\’’

Single Right Quote

Common Debugging Problems • Misleading compiler error messages – Syntax errors indicated on one-line may actually reflect an error made on an earlier line

• Capitalization errors – Java is case sensitive, identifier names must use the same capitalization rules each time

• Logic Errors – Program appears to run correctly, but on closer inspection the wrong output is displayed

Limitations of Numeric Variables • Unlike the integers mathematics the type int is not infinitely large and it is possible to compute a value incorrectly because the value is too large to be stored in an int variable storage location • Unlike the real numbers in mathematics the type double is not dense, it is not always possible to test double expressions for equality and obtain a correct result due to rounding errors in representations

Mixing Numeric Data Types • Java will automatically convert int expressions to double values without loss of information int i = 5; double x = i + 10.5; • To convert double expressions to int requires a typecasting operation and truncation will occur i = (int) (10.3 * x)

• To round-up instead of truncating add 0.5 i = (int) (10.3 * x + 0.5)

Mixed Mode Operations and Strings • It is important to remember that “13” and 13 are not the same • Examples out.println(“4” + “5”) // prints 45 out.println(“4” + 5) // prints 45 out.println(4 + 5) // prints 9

Characters as Integers • It is legal to assign a char to an int variable int i = ‘a’; // assigns 97 to i • It is legal to assign an int to an char variable char c = 97; // assigns ‘a’ to c • It is possible to perform arithmetic on char variables char ch = ‘a’; ch = ch + 1; // assigns ‘b’ to ch