1 Chapter 2: Java Fundamentals cont’d Spring 2006-2007 Lory Al Moakar.
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Transcript of 1 Chapter 2: Java Fundamentals cont’d Spring 2006-2007 Lory Al Moakar.
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Chapter 2: Java Fundamentals cont’d
Spring 2006-2007Lory Al Moakar
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Outline 2.1 The Parts of a Java Program 2.2 The print and println Methods, and the Java Standard Class
Library 2.3 Variables and Literals 2.4 Primitive Data Types 2.5 Arithmetic Operators 2.6 Combined Assignment Operators 2.7 Conversion Between Primitive Types 2.8 Creating Named Constants with final 2.9 The String Class 2.10 Scope 2.11 Comments 2.12 Programming Style 2.13 Reading Keyboard Input 2.14 Dialog Boxes 2.15 Common Errors to Avoid
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Review
Parts of the program Comments: start with //
Are ignored by the compiler Class header : public class Name Method header:
public static void main( String args[] ) Statements
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Review
System.out.print: displays on the screen what we put in “”
System.out.println: same as print except that it moves the cursor to a new line after displaying the text
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ReviewMoves the cursor to
\n a new line
\t the next tab stop
\b one character back
\r To the beginning of the line
\\ Prints a backslash
\’ Prints a single quote
\” Prints a double quotation mark
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Review
Variables: Declare: type and identifier Initialize: give it value ~ literal
Literals: Identifiers:
Start with letter, _, or $ Have only numbers, letters, _ and $ Cannot be a keyword
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Printing a variable
2 ways: On its own:
System.out.println( identifier); Combined with text:System.out.println( “The result is: “+
identifier );
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Example// This program has a variable.
public class Variable{ public static void main(String[] args) { int value;
value = 5; System.out.print("The value is "); System.out.println(value); }}
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2.4 Primitive Data Types
Each variable has a data type which is the type of data that can be stored in the memory location allocated
Here is a list of primitive(numeric) data types:
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2.4 Primitive Data Types cont’dData type
Size Range
byte 1 byte Integer between -128 to 127
short 2 bytes Integer between -215 to 215 -1
int 4 bytes Integer between -231 to 231 -1
long 8 bytes Integer between -263 to 263 -1
float 4 bytes Floating point numbers with 7 digits of accuracy
double 8 bytes Floating point numbers with 15 digits of accuracy
No digits after decimal point
15 digits after decimal point
7 digits after decimal point
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Declaration revisited
Datatype Variablename; Examples:
int hours; byte minutes; short month; float average; double distance
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The Integer Data Types// This program has variables of several of the integer types.
public class IntegerVariables{ public static void main(String[] args) { int checking; // Declare an int variable named checking. byte miles; // Declare a byte variable named miles. short minutes; // Declare a short variable named minutes. long days; // Declare a long variable named days.
checking = -20; miles = 105; minutes = 120; days = 185000; System.out.println("We have made a journey of " + miles + " miles."); System.out.println("It took us " + minutes + " minutes."); System.out.println("Our account balance is $" + checking); System.out.println("About " + days + " days ago Columbus " + "stood on this spot."); }}
We have made a journey of 105 miles.It took us 120 minutes.Our account balance is $-20.About 185000 days ago Columbus stood on this spot.No Commas
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The Floating Data Types// This program demonstrates the double data type.
public class Sale{ public static void main(String[] args) { double price, tax, total;
price = 29.75; tax = 1.76; total = 31.51; System.out.println("The price of the item " + "is " + price); System.out.println("The tax is " + tax); System.out.println("The total is " + total); }}
The price of the item is 29.75The tax is 1.76The total is 31.15
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The Floating Data Types
float number = 23.5; float number = 23.5f; float number = 23.5F;
ERROR
CORRECT
CORRECT
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The boolean Data Type a boolean variable can have two values:
true false
Example:boolean bool;bool = true;System.out.println(bool);bool = false;System.out.println(bool);
truefalse
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The char Data Type used to store characters character literals are enclosed in single
quotes Example:
char letter;letter = 'A';System.out.println(letter);letter = 'B';System.out.println(letter);
AB
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The char Data Type
Characters are internally represented by numbers.
Java uses Unicode which is a set of numbers that are used as codes for representing characters
The codes are found in appendix A on the CD
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Example
char letter; letter = 65; System.out.println(letter) letter = 66; System.out.println(letter);
A B
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Variable Assignment and Initialization
assignment statement is used to put a value into a variable. Ex: x = 15;
always put the identifier on the left of the equal sign and the literal to the right of the equal sign. Ex: 15 = x; is incorrect
you can assign the value of one identifier to another. Ex: x = y; now x has the value stored in y
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Valid Variable Declaration
int month =2, days = 28; float distance = 35.2f; int c = 8, y =10, x, v=2;
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2.5 Arithmetic Operators
3 types of operator: unary: require a single operand.
There is one unary operand: -9 (the negation operator)
--5 is 5 binary: require two operands ternary: require three operands
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Arithmetic operatorsOperator Meaning Type Example
+ Addition Binary total = cost+tax;
- Subtraction Binary cost = total-tax;
* Multiplication Binary Tax = cost*rate;
/ Division Binary saleprice=original/2;
% Modulus Binary remainder=value%3;
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Examples of Statements with Arithmetic Operators
amount = x + y; amount = 562+543; Minutes = 800 – call; Tip = bill * 0.18; Slice = cake /8;
Notice that the identifier is to the
left of the =
Notice that the arithmetic operator
is to the right of the =
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Example
int counter = 0; //counter =0counter = counter + 1; //counter =1counter = counter + 39; //counter=40counter = counter – 8; //counter=32counter = counter * 5; //counter=160counter = counter / 2; //counter= 80
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The % operator
Returns the remainder of the division Examples;
4%5 is 4 30%6 is 0 22%7 is 1 3205%100 is 5 3205%10 is 5
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Exercise
Write the following in a Java file:double amount = 137/5;
System.out.println(“Amount is : “ + amount );
amount = 137.0/5; System.out.println(“Amount is : “ +
amount );
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Integer Division
Dividing an integer by an integer gives an integer the remainder is ignored
Examples: 5/4 is 1 17/3 is 5
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Operator Precedence
What is the result of: Polynomial = 1+2*3+ 6/2 -2; Is it ?
(1+2)*3 + 6/(2-2) 1+(2*3) +(6/2)-2 (1+2)*3 + (6/2)-2
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Precedence Rules
Always evaluate * , / and % before + and –
Always negate before any calculations *, / and % have same precedence + and – have same precedence If equal precedence then evaluate
from left to right except for negations where we evaluate from right to left
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Precedence examples
Polynomial = 1+2*3+ 6/2 – 2; Polynomial has the value of 1+6+3-2=8
Polynomial = –1 + 5 – 2; // 2 Polynomial = –(–3) + –(–5); //8
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Grouping with parentheses
You can use parentheses to force the evaluation of a formula
Examples: x * ( y + z*z ) instead of x*y + z*z x * ( y * ( z + 165 ) + 85 ) – 65 Average = (a +b +c ) /3;
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The Math class
value = Math.pow( x,y); // now value holds x to the power of y
value = Math.sqrt( x); //now value holds the square root of x
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Combined Assignment Operators
+= x += 1; x = x + 1;
–= x –= 1; x = x – 1;
*= x *= 1; x = x * 1;
/= x /= 1; x = x / 1;
%= x %= 1; x = x % 1;