Chapter 2 Introduction to Java Applications; Input/Output and Operators Java™ How to Program, 10/e © Copyright 1992-2015 by Pearson Education, Inc. All.

Chapter 2 Introduction to Java Applications; Input/Output and Operators
Java™ How to Program, 10/e © Copyright by Pearson Education, Inc. All Rights Reserved.

2.1 Introduction Java application programming
Use tools from the JDK to compile and run programs. Videos at Help you get started with Eclipse, NetBeans and IntelliJ IDEA integrated development environments. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.2 Your First Program in Java: Printing a Line of Text
Java application A computer program that executes when you use the java command to launch the Java Virtual Machine (JVM). Sample program in Fig. 2.1 displays a line of text. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.2 Your First Program in Java: Printing a Line of Text (Cont.)
Commenting Your Programs Comments // Fig. 2.1: Welcome1.java // indicates that the line is a comment. Used to document programs and improve their readability. Compiler ignores comments. A comment that begins with // is an end-of-line comment—it terminates at the end of the line on which it appears. Traditional comment, can be spread over several lines as in /* This is a traditional comment. It can be split over multiple lines */ This type of comment begins with /* and ends with */. All text between the delimiters is ignored by the compiler. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.2 Our First Program in Java: Printing a Line of Text (Cont.)
Javadoc comments Delimited by /** and */. All text between the Javadoc comment delimiters is ignored by the compiler. Enable you to embed program documentation directly in your programs. The javadoc utility program (online Appendix G) reads Javadoc comments and uses them to prepare program documentation in HTML format. © Copyright by Pearson Education, Inc. All Rights Reserved.

Using Blank Lines Blank lines, space characters and tabs Make programs easier to read. Together, they’re known as white space (or whitespace). White space is ignored by the compiler. © Copyright by Pearson Education, Inc. All Rights Reserved.

Declaring a class Class declaration public class Welcome1 Every Java program consists of at least one class that you define. class keyword introduces a class declaration and is immediately followed by the class name. Keywords (Appendix C) are reserved for use by Java and are always spelled with all lowercase letters. For example: public, static, class, void. © Copyright by Pearson Education, Inc. All Rights Reserved.

Filename for a public Class A public class must be placed in a file that has a filename of the form ClassName.java, so class Welcome1 is stored in the file Welcome1.java. © Copyright by Pearson Education, Inc. All Rights Reserved.

Class Names and Identifiers A class name is an identifier—a series of characters consisting of letters, digits, underscores (_) and dollar signs ($) that does not begin with a digit and does not contain spaces. Java is case sensitive—uppercase and lowercase letters are distinct—so a1 and A1 are different (but both valid) identifiers. By convention, begin with a capital letter and capitalize the first letter of each word they include (e.g., SampleClassName). © Copyright by Pearson Education, Inc. All Rights Reserved.

Declaring the main method public static void main( String[] args ) Starting point of every Java application. Parentheses after the identifier main indicate that it’s a program building block called a method. Java class declarations normally contain one or more methods. main must be defined as shown; otherwise, the JVM will not execute the application. Methods perform tasks and can return information when they complete their tasks. Keyword void indicates that this method will not return any information. © Copyright by Pearson Education, Inc. All Rights Reserved.

Body of the method declaration Enclosed in left and right braces. Statement System.out.println("Welcome to Java Programming!"); Instructs the computer to perform an action Display the characters contained between the double quotation marks. Together, the quotation marks and the characters between them are a string—also known as a character string or a string literal. White-space characters in strings are not ignored by the compiler. Strings cannot span multiple lines of code. © Copyright by Pearson Education, Inc. All Rights Reserved.

System.out object Standard output object. Allows a Java application to display information in the command window from which it executes. System.out.println method Displays (or prints) a line of text in the command window. The string in the parentheses the argument to the method. Positions the output cursor at the beginning of the next line in the command window. Most statements end with a semicolon. © Copyright by Pearson Education, Inc. All Rights Reserved.

Compiling Your First Java Application Open a command window and change to the directory where the program is stored. Many operating systems use the command cd to change directories. To compile the program, type javac Welcome1.java If the program contains no compilation errors, preceding command creates a.class file (known as the class file) containing the platform- independent Java bytecodes that represent the application. When we use the java command to execute the application on a given platform, these bytecodes will be translated by the JVM into instructions that are understood by the underlying operating system. © Copyright by Pearson Education, Inc. All Rights Reserved.

Executing the Welcome1 Application To execute this program in a command window, change to the directory containing Welcome1.java—C:\examples\ch02\ fig02_01 on Microsoft Windows or ~/Documents/ examples/ch02/fig02_01 on Linux/OS X. Next, type java Welcome1. This launches the JVM, which loads the Welcome1.class file. The command omits the .class file-name extension; otherwise, the JVM will not execute the program. The JVM calls class Welcome1’s main method. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.3 Modifying Your First Java Program
Class Welcome2, shown in Fig. 2.3, uses two statements to produce the same output as that shown in Fig. 2.1. New and key features in each code listing are highlighted. System.out’s method print displays a string. Unlike println, print does not position the output cursor at the beginning of the next line in the command window. The next character the program displays will appear immediately after the last character that print displays. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.3 Modifying Your First Java Program (Cont.)
Newline characters indicate to System.out’s print and println methods when to position the output cursor at the beginning of the next line in the command window. Newline characters are whitespace characters. The backslash (\) is called an escape character. Indicates a “special character” Backslash is combined with the next character to form an escape sequence—\n represents the newline character. Complete list of escape sequences jls-3.html#jls © Copyright by Pearson Education, Inc. All Rights Reserved.

String concatenation // Three strings are concatenated
"Welcome " + "to " + "Java" // String Chapter is concatenated with number 2 "Chapter" + 2 // String Supplement is concatenated with character b "Supplement" + ‘b’ dr. Amal Khalifa,Fall14

Example : program output
Public class Test1 { public static void main(String args[]){ String msg; String msg2= + msg; System.out.print ("message1=“ + “ I"+“ Like“); System.out.println ("\n message 2="+“ Java“ + "\t"+ “end”); } © Copyright by Pearson Education, Inc. All Rights Reserved.

2.4 Displaying Text with printf
System.out.printf method f means “formatted” displays formatted data Multiple method arguments are placed in a comma-separated list. Calling a method is also referred to as invoking a method. Java allows large statements to be split over many lines. Cannot split a statement in the middle of an identifier or string. Method printf’s first argument is a format string May consist of fixed text and format specifiers. Fixed text is output as it would be by print or println. Each format specifier is a placeholder for a value and specifies the type of data to output. Format specifiers begin with a percent sign (%) and are followed by a character that represents the data type. Format specifier %s is a placeholder for a string. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.5 Another Application: Adding Integers
Whole numbers, like –22, 7, 0 and 1024) Programs remember numbers and other data in the computer’s memory and access that data through program elements called variables. The program of Fig. 2.7 demonstrates these concepts. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.6 Memory Concepts Programs remember numbers and other data in the computer’s memory and access that data through program elements called variables. Variables Every variable has a name, a type, a size (in bytes) and a value The name can be any valid identifier. A variable’s type specifies what kind of information is stored at that location in memory. The size depends on the type as in the language specification When a new value is placed into a variable, the new value replaces the previous value (if any) The previous value is lost, so this process is said to be destructive.

dr. Amal Khalifa,Fall14

4.14 Primitive Types Appendix D lists the eight primitive types in Java. Java requires all variables to have a type. Java is a strongly typed language. Primitive types in Java are portable across all platforms. Instance variables of types char, byte, short, int, long, float and double are all given the value 0 by default. Instance variables of type boolean are given the value false by default. Reference-type instance variables are initialized by default to the value null. © Copyright by Pearson Education, Inc. All Rights Reserved.

Data Types: numbers Integers Floating-point numbers
Whole numbers, like –22, 7, 0 and 1024. Floating-point numbers A number with a decimal point, such as 7.33, or ). Two types: float represents single-precision floating-point numbers up to seven significant digits. double variables can store numbers with larger magnitude and finer detail than float variables. * This part is described in [1] 4.13 dr. Amal Khalifa,Fall14

Declaring Variables Rule: Examples: <dataType> identifier;
int myValue; char response; float price; double yCoord; Must declare all data before use in program When a new value is placed into a variable, the new value replaces the previous value (if any)  The previous value is lost. dr. Amal Khalifa,Fall14

2.5.4 Declaring Variables to Store Integers
Variable declaration statements int number1; // first number to add int number2; // second number to add int sum; // sum of number1 and number2 declare that variables number1, number2 and sum hold data of type int They can hold integer. Range of values for an int is –2,147,483,648 to +2,147,483,647. The int values you use in a program may not contain commas. Several variables of the same type may be declared in one declaration with the variable names separated by commas. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.5.1 import Declarations Helps the compiler locate a class that is used in this program. Rich set of predefined classes that you can reuse rather than “reinventing the wheel.” Classes are grouped into packages—named groups of related classes—and are collectively referred to as the Java class library, or the Java Application Programming Interface (Java API). You use import declarations to identify the predefined classes used in a Java program. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.5 Another Application: Adding Integers (Cont.)
Scanner Enables a program to read data for use in a program. Data can come from many sources, such as the user at the keyboard or a file on disk. Before using a Scanner, you must create it and specify the source of the data. The equals sign (=) in a declaration indicates that the variable should be initialized (i.e., prepared for use in the program) with the result of the expression to the right of the equals sign. The new keyword creates an object. Standard input object, System.in, enables applications to read bytes of data typed by the user. Scanner object translates these bytes into types that can be used in a program. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.5.3 Declaring and Creating a Scanner to Obtain User Input from the Keyboard
Variable declaration statement Scanner input = new Scanner( System.in ); Specifies the name (input) and type (Scanner) of a variable that is used in this program. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.5.5 Prompting the User for Input
Output statement that directs the user to take a specific action. Class System Part of package java.lang. Class System is not imported with an import declaration at the beginning of the program. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.5.6 Obtaining an int as Input from the User
Scanner method nextInt number1 = input.nextInt(); // read first number from user Obtains an integer from the user at the keyboard. Program waits for the user to type the number and press the Enter key to submit the number to the program. The result of the call to method nextInt is placed in variable number1 by using the assignment operator, =. “number1 gets the value of input.nextInt().” Operator = is called a binary operator—it has two operands. Everything to the right of the assignment operator, =, is always evaluated before the assignment is performed. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.5 Another Application: Adding Integers (Cont.)
Arithmetic sum = number1 + number2; // add numbers then store total in sum Assignment statement that calculates the sum of the variables number1 and number2 then assigns the result to variable sum by using the assignment operator, =. “sum gets the value of number1 + number2.” Portions of statements that contain calculations are called expressions. An expression is any portion of a statement that has a value associated with it. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.5.9 Displaying the Result of the Calculation
Integer formatted output System.out.printf( "Sum is %d%n", sum ); Format specifier %d is a placeholder for an int value The letter d stands for “decimal integer.” © Copyright by Pearson Education, Inc. All Rights Reserved.

2.7 Arithmetic Arithmetic operators are summarized in Fig. 2.11.
The asterisk (*) indicates multiplication The percent sign (%) is the remainder operator The arithmetic operators are binary operators because they each operate on two operands. Integer division yields an integer quotient. Any fractional part in integer division is simply truncated (i.e., discarded)—no rounding occurs. The remainder operator, %, yields the remainder after division. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.7 Arithmetic (Cont.) Arithmetic expressions in Java must be written in straight-line form to facilitate entering programs into the computer. Expressions such as “a divided by b” must be written as a / b, so that all constants, variables and operators appear in a straight line. Parentheses are used to group terms in expressions in the same manner as in algebraic expressions. If an expression contains nested parentheses, the expression in the innermost set of parentheses is evaluated first. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.7 Arithmetic (Cont.) Rules of operator precedence
Multiplication, division and remainder operations are applied first. If an expression contains several such operations, they are applied from left to right. Multiplication, division and remainder operators have the same level of precedence. Addition and subtraction operations are applied next. If an expression contains several such operations, the operators are applied from left to right. Addition and subtraction operators have the same level of precedence. When we say that operators are applied from left to right, we are referring to their associativity. Some operators associate from right to left. Complete precedence chart is included in Appendix A. © Copyright by Pearson Education, Inc. All Rights Reserved.

Java Basics: Expressions
Examples: 5 / 2 yields an integer 2. 5.0 / 2 yields a double value 2.5 5 % 2 yields 1 (the remainder of the division) Remainder is very useful in programming. an even number % 2 is always 0 and an odd number % 2 is always 1. So you can use this property to determine whether a number is even or odd dr. Amal Khalifa,Fall14

Individual Arithmetic Precision
Calculations done "one-by-one" 1 / 2 / 3.0 / 4 performs 3 separate divisions. Precision of Calculations "Highest-order operand" determines type of arithmetic "precision" performed Examples: 17 / 5 evaluates to ?? Both operands are integers Integer division is performed! 17.0 / 5 equals ?? Highest-order operand is "double type" Double "precision" division is performed! First 1 / 2 equals 0 Then 0 / 3.0 equals 0.0 Then 0.0 / 4 equals 0.0! You may give examples dr. Amal Khalifa,Fall14

More examples What is the order of evaluation in the following expressions? 3 + 4 * / 2 1 2 3 4 3 1 4 2 3 / (4 + 5) - 6 % 2 2 1 4 3 Find the answer by hand calculations 3 / (4 * (5 + (6 - 2))) 4 3 2 1 dr. Amal Khalifa,Fall14

Case study: Writing Expressions
Write a program that computes and displays the result of the following expressions 3 + 4 * / 2 3 / (4 + 5) - 6 % 2 Write a program No variables should be used 3 / (4 * (5 + (6 - 2))) dr. Amal Khalifa,Fall14

2.7 Arithmetic (Cont.) As in algebra, it’s acceptable to place redundant parentheses (unnecessary parentheses) in an expression to make the expression clearer. © Copyright by Pearson Education, Inc. All Rights Reserved.

Arithmetic Expressions
is translated to (3+4*x)/5 – 10*(y-5)*(a+b+c)/x + 9*(4/x + (9+x)/y) How to write arithmetic expressions dr. Amal Khalifa,Fall14

Java basics : Assigning Data
Initializing data in declaration statement Java’s default value for new variables is 0! int myValue = 10; Assigning data during execution Lvalues (left-side) & Rvalues (right-side) Lvalues must be variables Rvalues can be any expression Example: distance = rate * time; Lvalue: distance Rvalue: rate * time dr. Amal Khalifa,Fall14

Data Assignment Rules Compatibility of Data Assignments
intVar = 2.99; // 2 is assigned to intVar! Only integer part "fits", so that’s all that goes Called "implicit" or "automatic type conversion" Literals 2, 5.75, ‘Z’, "Hello World" Considered constants : can’t change in program Type mismatches General Rule: Cannot place value of one type into variable of another type dr. Amal Khalifa,Fall14

Type Casting Two types Implicit—also called "Automatic"
Done FOR you, automatically 17 / 5.5 Explicit type conversion Programmer specifies conversion with cast operator (double)17 / 5.5 (double)myInt / myDouble Explicitly "casts" or "converts" intVar to double type Result of conversion is then used Can add ".0" to literals to force precision arithmetic, but what about variables? We can’t use "myInt.0"! dr. Amal Khalifa,Fall14

Strings & Text String msg1 = new String( “Hello” );
What about strings? String msg1 = new String( “Hello” ); String msg2 = “Hello” ; String msg3 = “Year “ ; //valid??

4.12 Compound Assignment Operators
Compound assignment operators abbreviate assignment expressions. Statements like variable = variable operator expression; where operator is one of the binary operators +, -, *, / or % can be written in the form variable operator= expression; Example: c = c + 3; can be written with the addition compound assignment operator, +=, as c += 3; The += operator adds the value of the expression on its right to the value of the variable on its left and stores the result in the variable on the left of the operator. © Copyright by Pearson Education, Inc. All Rights Reserved.

4.13 Increment and Decrement Operators
Unary increment operator, ++, adds one to its operand Unary decrement operator, --, subtracts one from its operand An increment or decrement operator that is prefixed to (placed before) a variable is referred to as the prefix increment or prefix decrement operator, respectively. An increment or decrement operator that is postfixed to (placed after) a variable is referred to as the postfix increment or postfix decrement operator, respectively. © Copyright by Pearson Education, Inc. All Rights Reserved.

4.12 Increment and Decrement Operators (Cont.)
Using the prefix increment (or decrement) operator to add (or subtract) 1 from a variable is known as preincrementing (or predecrementing) the variable. Preincrementing (or predecrementing) a variable causes the variable to be incremented (decremented) by 1; then the new value is used in the expression in which it appears. Using the postfix increment (or decrement) operator to add (or subtract) 1 from a variable is known as postincrementing (or postdecrementing) the variable. This causes the current value of the variable to be used in the expression in which it appears; then the variable’s value is incremented (decremented) by 1. © Copyright by Pearson Education, Inc. All Rights Reserved.

No difference because of braces !!
Example int n=2, res; res = 2 * (n++); /*what is the value of res and n?*/ int n = 2, res; res = 2 * (++n); /*what is the value of res and n?*/ Post-Increment Pre-Increment No difference because of braces !! What if removed?? dr. Amal Khalifa,Fall14

Printf Conversion-Characters

Constants A “constant variable” is an identifier that is similar to a variable except that it holds one value for its entire existence Why constants: give names to otherwise unclear literal values facilitate changes to the code prevent inadvertent errors In Java: final double PI = ; dr. Amal Khalifa,Fall14

Example dr. Amal Khalifa,Fall14

2.8 Decision Making: Equality and Relational Operators
Condition An expression that can be true or false. if selection statement Allows a program to make a decision based on a condition’s value. Equality operators (== and !=) Relational operators (>, <, >= and <=) Both equality operators have the same level of precedence, which is lower than that of the relational operators. The equality operators associate from left to right. The relational operators all have the same level of precedence and also associate from left to right. © Copyright by Pearson Education, Inc. All Rights Reserved.

2.8 Decision Making: Equality and Relational Operators (Cont.)
An if statement always begins with keyword if, followed by a condition in parentheses. Expects one statement in its body, but may contain multiple statements if they are enclosed in a set of braces ({}). The indentation of the body statement is not required, but it improves the program’s readability by emphasizing that statements are part of the body. Note that there is no semicolon (;) at the end of the first line of each if statement. Such a semicolon would result in a logic error at execution time. Treated as the empty statement—semicolon by itself. © Copyright by Pearson Education, Inc. All Rights Reserved.

Debugging errors are called bugs.
When you type a program, typos and unintentional syntax errors are likely to occur. Therefore, when you compile a program, the compiler will identify the syntax errors. Debugging means to identify and fix syntax errors. dr. Amal Khalifa,Fall14

Find and fix error!! class Test2 {
public static void main (String[] args) { System.out.println("*\n java \n*”); System.out.println("I" * ‘Love’); System.out.println(3 + 2) } © Copyright by Pearson Education, Inc. All Rights Reserved.

Program Style Always use comments… Identifier naming
Make programs easy to read and modify // Two slashes indicate entire line is to be ignored /*Delimiters indicates everything between is ignored*/ Identifier naming ALL_CAPS for constants lowerToUpper for variables Most important: MEANINGFUL NAMES! dr. Amal Khalifa,Fall14

Chapter 2 Introduction to Java Applications; Input/Output and Operators Java™ How to Program, 10/e © Copyright 1992-2015 by Pearson Education, Inc. All.

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Chapter 2 Introduction to Java Applications; Input/Output and Operators Java™ How to Program, 10/e © Copyright 1992-2015 by Pearson Education, Inc. All.

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Presentation on theme: "Chapter 2 Introduction to Java Applications; Input/Output and Operators Java™ How to Program, 10/e © Copyright 1992-2015 by Pearson Education, Inc. All."— Presentation transcript:

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