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Basics and arrays

Basics and arrays. Operators: Arithmetic: +, -, *, /, % Relational: <, <=, >, >=, ==, != Logical: &&, ||, ! Primitive data types Byte(8), short(16), int(32), long(64), float(32), double(64), boolean Numeric type conversion float f = (float)10; int I = (int)f;. Control structure.

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Basics and arrays

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  1. Basics and arrays • Operators: • Arithmetic: +, -, *, /, % • Relational: <, <=, >, >=, ==, != • Logical: &&, ||, ! • Primitive data types • Byte(8), short(16), int(32), long(64), float(32), double(64), boolean • Numeric type conversion • float f = (float)10; • int I = (int)f;

  2. Control structure • Selection if( condition ) { statements; } else { statements; } Switch( integer) { Case 1: statements; Case 2: statements; … Default: .. } • Repetition • while( condition) { … } • do { • …. • }while(condition); • for ( x = 0; x < 10; x++) • { • statements; • }

  3. String type: String • String is a predefined class in the Java library • It is not primitive data type • It is known as a reference type • Declare a string • String message = “welcome!”; • Concatenate strings • String s = “Chapter”+2; • message +=“ and Java is fun”; • System.out.println(“i+j is” +(i+j)); // i=1, j = 2

  4. Getting input from input Dialogs • String input = JOptionPane.showInputDialog(null, “Enter an input”, “Input Dialog memo”, JOptionPane.QUESTION_MESSAGE); • JOptionPane.showMessageDialog(null, input, “Example”, JOptionPane.INFORMATION_MESSAGE); • Converting string to numbers • int val = Integer.parseInt(input); • double d = Double.parseDouble(input);

  5. Methods • Creating a method: • modifier returntype methodname(list of parameters) • { • } • public static int max( int int1, int int2) • { • if( int1 > int2) return int1; • else retun int2; • } • primitive data are passed by value ( No Pointer!)

  6. Calling a method • int larger = max(3,4); • System.out.println(max(3,4)); • Static method can be called directly, it doesn’t need a class object to call it • In the same class, it can be called by the method name • In other class definition, it can be called by ClassName.max(3,4);

  7. The Math class • public static double sin(double x) • public static double cos( double x) • public static double exp( double a) • public static double log( double a) • public static double pow( double a, double b) • public static double sqrt( double a) • Min, max, abs and random methods

  8. The random methed • Math.random() generate a random double number 0<= Math.random <1.0 • Generate random number between 0 and 9 • int I = (int)(Math.random()*10); • Generate number between 50 and 99 • Int I = 50 + (int)(Math.random()*50); • In genral, generate any random number between a and a+b, excluding a+b • a + Math.random()*b

  9. Generate random characters • Every character has a unique Unicode between 0 and FFFF in hexadecimal (65535) in decimal • Generate random integer between 0 – 65535 • (int) (Math.random()*(65535+1) • Generate random lower case letter • Unicode for a (int) ‘a’ • Unicode for z is (int) ‘z’ • Random letter between a-z • (char) (‘a’ + Math.random()*(‘z’ =‘a’ +1))

  10. Guess a number • Write a program that generate a random number between 0-100 • Ask user to guess it, • Print message that state either the number user guess is higher, lower • Repeat until user enter the correct nmber.

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