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Windows Programming Using Java 1 Chapter2: Introduction to Java Applications INSTRUCTOR: SHIH-SHINH HUANG Contents 2 Introduction A First Program in Java Text Displaying Value Input: Integer Addition Arithmetic Equality and Relational Operators Introduction 3 Java Keywords abstract do import public throws boolean double instanceof return transient break else int short try byte extends interface static void case final long strictfp volatile catch finally native super while char float new switch class for package synchronized continue if private this default implements protected throw Introduction 4 Identifier Rule Series of characters consisting of letters, digits, underscores ( _ ) and dollar signs ( $ ) Identifier = (letter | '_' | ' $ ') {letter | digit | '_'}. “Welcome1”, “7button” Case a1 “$value”, “_value”, “button7” are valid is invalid sensitive (capitalization matters) and A1 are different Introduction 5 Primitive Data Type Data Type Purpose Contents Default Value* boolean Truth value true or false fales char Character Unicode characters \u0000 byte Signed integer 8 bit two's complement (byte) 0 short Signed integer 16 bit two's complement (short) 0 int Signed integer 32 bit two's complement 0 long Signed integer 64 bit two's complement 0L float Real number 32 bit IEEE 754 floating point 0.0f double Real number 64 bit IEEE 754 floating point 0.0d A First Program in Java 6 Function: printing a line of text 1 2 3 4 5 6 7 8 9 10 11 12 13 // Fig. 2.1: Welcome1.java // Text-printing program. public class Welcome1 { // main method begins execution of Java application public static void main( String args[] ) { System.out.println( "Welcome to Java Programming!" ); } // end method main } // end class Welcome1 Welcome to Java Programming! A First Program in Java 7 Comments // remainder of line is comment Comments ignored Document and describe code 1 // Fig. 2.1: Welcome1.java Multiple line comments: /* ... */ /* This is a multiple line comment. It can be split over many lines */ A First Program in Java 8 Class Declaration 4 public class Welcome1 { Every Java program has at least one defined class Keyword: class The words reserved for use by Java keyword followed by class name class name has to be an identifier Naming Convention: capitalize every word Example: SampleClassName A First Program in Java 9 Body Delimiter Left brace { Begins body of every class A corresponding right brace “}” ends definition (line 13) 4 public class Welcome1 { 13}/* End of Class Welcome1 */ Indentation Convention Whenever you type an left brace “{“, immediately type the right brace “}”. Then, indent to begin type the body. A First Program in Java 10 Program Entry Applications begin executing at main() Exactly one method must be called main Parenthesis indicate main is a method Java applications contain one or more methods 5 public static void main( String args[] ) Methods can perform tasks and return result means main returns no information args[]:input arguments in String data type. void: A First Program in Java 11 Statements Statements are instructions to commend hardware to perform some operations. It must end with semicolon “;” 7 System.out.println("Welcome to Java Programming!" ); standard output object System.out.println: displays line of text System.out: A First Program in Java 12 Execution Steps JAVA PROGRAM EXECUTION Java source code Java compiler Welcome.java javac Welcome.java byte-code .class byte-code interpreter JVM java Welcome EXECUTION A First Program in Java 13 Execution Steps Compiling a program Open a command window, go to program’s directory. Type javac Welcome.java If no errors, Welcome.class created Executing a program Type java Welcome to start JVM and then run the program Welcome.class Interpreter calls method main A First Program in Java 14 Demonstration 4 5 6 7 8 9 10 11 12 13 public class Welcome1 { // main method begins execution of Java application public static void main( String args[] ) { System.out.println( "Welcome to Java Programming!" ); } // end method main } // end class Welcome1 Text Displaying 15 Displaying Methods System.out.println Prints argument, puts cursor on new line System.out.print Prints argument, keeps cursor on same line System.out.printf Prints 7 8 argument which is a format string System.out.print("Welcome toto “); System.out.println("Welcome Java System.out.println(“JavaProgramming!" Programming!"); ); Text Displaying 16 Escape Sequences The backslash “\” is called an escape character to indicate a “special character” is to be output. Backslash combined with character makes escape sequence. Escape Sequence Description \n Newline \t Horizontal Tab \r Carriage Return. Position the cursor at the beginning of the current line \\ Backslash \” Double Quote Text Displaying 17 Escape Sequences 7 System.out.println("Welcome\nto\nJava\n Programming!" ); Welcome to Java Programming! 7 System.out.println(“\”in quotes\”" ); “in quotes” Text Displaying 18 Format String The first argument of printf() is a format string Fixed Text Format Specifier Format specifier is a placeholder for a value and specifies the type of data. Percent Sign (“%”) Data Type Text Displaying 19 Format String 7 Type Character Input String Result %c char character %d signed int signed decimal integer %f float real number, standard notation %s string string System.out.printf(“%s\n%s\n”, “Welcome to”, “Java Programming!" ); Welcome to Java Programming! Value Input: Integer Addition 20 Requirements Read in two integers from users Compute the summation of them Print out the result on the screen Enter first integer:1 Enter second integer:3 Sum is: 4 Value Input: Integer Addition 21 Variable Declaration Every variable has a name, a type, a size and a value Name corresponds to location in memory When new value is placed into a variable, replaces (and destroys) previous value Reading them from memory does not change them int number1=10; int number1; number1=10; Value Input: Integer Addition 22 Variable Declaration public class Addition { // main method begins execution of Java application public static void main( String args[] ){ int number1; int number2; int sum; …… …… }/* End of main */ }/* End of class Addition */ Value Input: Integer Addition 23 import java.util.Scanner; public class Addition { // main method begins execution of Java application public static void main( String args[] ){ …… // create Scanner to obtain input from command window Scanner input = new Scanner( System.in ); // read the first integer System.out.print("Enter first integer:"); number1 = input.nextInt(); // read the second integer System.out.print("Enter second integer:"); number2 = input.nextInt(); …… }/* End of main */ }/* End of class Addition */ Value Input: Integer Addition 24 import java.util.Scanner; public class Addition { // main method begins execution of Java application public static void main( String args[] ){ …… sum = number1 + number2; System.out.printf("Sum is: %d\n", sum);}/* End of main */ }/* End of class Addition */ Arithmetic 25 Description Arithmetic calculations used in most programs Asterisk ‘*’ indicates multiplication Percent sign ‘%’ is the remainder (modulus) operator Integer division truncates remainder 7 / 5 evaluates to 1 Modulus operator % returns the remainder 7 % 5 evaluates to 2 Arithmetic 26 Operator precedence Some arithmetic operators act before others Operator(s) Operation(s) Order of evaluation (precedence) () Parentheses *, /, or % Multiplication Division Modulus Addition Subtraction Evaluated first. If the parentheses are nested, the expression in the innermost pair is evaluated first. If there are several pairs of parentheses “on the same level” (i.e., not nested), they are evaluated left to right. Evaluated second. If there are several, they are evaluated left to right. Evaluated last. If there are several, they are evaluated left to right. + or - Equality and Relational Operators 27 Description A condition is an expression that can be either true or false. It is used in control statements (if, for, while) to change the execution flow of program Conditions Equality can be formed by using Operators Relational Operators Equality and Relational Operators 28 Equality/Relational Operators Standard Algebraic Java Equality Sample Meaning = == x == y x is equal to y? != x != y x is not equal to y ? > > x>y x is greater than y ? < < x<y x is less than y? >= x >= y x is greater than or equal to y <= x <= y x is less than or equal to y Equality and Relational Operators 29 Example import java.util.Scanner; public class Comparison { public static void main( String args[] ){ int number1=100; int number2=200; if(number1 == number2){ System.out.printf(“%d == %d \n”, number1, number2); }/* End of if-condition */ if(number1 != number2){ System.out.printf(“%d != %d \n”, number1, number2); }/* End of if-condition */ }/* End of main */ }/* End of class Addition */ 30 www.themegallery.com