OOP-Lecture Java Loop Controls: 1 Lecturer: Hawraa Sh. You can use one of the following three loops: while Loop do...while Loop for Loop

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1 Java Loop Controls: You can use one of the following three loops: while Loop do...while Loop for Loop 1- The while Loop: A while loop is a control structure that allows you to repeat a task a certain number of times. Syntax: The syntax of a while loop is: while(boolean_expression) { //Statements int x =10; while( x <20){ System.out.print("value of x : "+ x ); x++; 2- The do...while Loop: A do...while loop is similar to a while loop, except that a do...while loop is guaranteed to execute at least one time. Syntax: The syntax of a do...while loop is: do { //Statements while(boolean_expression); 1 Lecturer: Hawraa Sh.

2 int x =10; do{ System.out.print("value of x : "+ x ); x++; while( x <20); 3-The for Loop: A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times. A for loop is useful when you know how many times a task is to be repeated. Syntax: The syntax of a for loop is: for(initialization;boolean_expression; update) { //Statements for(int x =10; x <20; x = x+1){ System.out.print("value of x : "+ x ); The break Keyword: The break keyword is used to stop the entire loop. The break keyword must be used inside any loop or a switch statement. Syntax: The syntax of a break is a single statement inside any loop: break; 2 Lecturer: Hawraa Sh.

3 for(int x =10; x <50; x = x+10){ if( x ==30){ break; System.out.print( x ); The output: The continue Keyword: The continue keyword can be used in any of the loop control structures. It causes the loop to immediately jump to the next iteration of the loop. In a for loop, the continue keyword causes flow of control to immediately jump to the update statement. In a while loop or do/while loop, flow of control immediately jumps to the Boolean expression. Syntax: The syntax of a continue is a single statement inside any loop: continue; for(int x =10; x <=50; x = x+10){ if( x ==30){ continue; System.out.print( x ); The output: Lecturer: Hawraa Sh.

4 Java Characters: Normally, when we work with characters, we use primitive data types char. char ch ='a'; Character Methods: isletter( ) Determines whether the specified char value is a letter. isdigit( ) Determines whether the specified char value is a digit. iswhitespace( ) Determines whether the specified char value is white space. isuppercase( ) Determines whether the specified char value is uppercase. islowercase( ) Determines whether the specified char value is lowercase. touppercase( ) Returns the uppercase form of the specified char value. tolowercase( ) Returns the lowercase form of the specified char value. tostring( ) Returns a String object representing the specified character value that is, a one-character string. All these Methods call after character.method System.out.println(Character.isLetter('c')); System.out.println(Character.isLetter('5')); System.out.println(Character.isDigit('c')); System.out.println(Character.isDigit('5')); 4 Lecturer: Hawraa Sh.

5 System.out.println(Character.isWhitespace('c')); System.out.println(Character.isWhitespace(' ')); System.out.println(Character.isWhitespace('\n')); System.out.println(Character.isWhitespace('\t')); System.out.println( Character.isUpperCase('c')); System.out.println( Character.isUpperCase('C')); System.out.println( Character.isUpperCase('\n')); System.out.println( Character.isUpperCase('\t')); System.out.println(Character.isLowerCase('c')); System.out.println(Character.isLowerCase('C')); System.out.println(Character.isLowerCase('\n')); System.out.println(Character.isLowerCase('\t')); 5 Lecturer: Hawraa Sh.

6 System.out.println(Character.toUpperCase('c')); System.out.println(Character.toUpperCase('C')); C C System.out.println(Character.toLowerCase('c')); System.out.println(Character.toLowerCase('C')); c c Java Strings: Strings which are widely used in Java programming are a sequence of characters. In the Java programming language, strings are objects. Creating Strings: The most direct way to create a string is to write: String greeting ="Hello world!"; String Length: length ( ) method returns the number of characters contained in the string object. publicclassstringdemo{ String s ="second class"; int len = s.length(); System.out.println("String Length is : "+ len ); This would produce the following result: String Length is :12 6 Lecturer: Hawraa Sh.

7 String Methods: char charat (int index) Returns the character at the specified index. String concat(string str) Concatenates the specified string to the end of this string. int indexof(int ch) Returns the index within this string of the first occurrence of the specified character. int indexof(string str) Returns the index within this string of the first occurrence of the specified substring. int length( ) Returns the length of this string. String replace(char oldchar, char newchar) Returns a new string resulting from replacing all occurrences of oldchar in this string with newchar. String tolowercase( ) Converts all of the characters in this String to lower case using the rules of the default locale. String touppercase() Converts all of the characters in this String to upper case using the rules of the default locale. String s = "Strings are immutable"; char result = s.charat(8); System.out.println(result); a String s = "Strings are immutable"; s = s.concat(" all the time"); System.out.println(s); Strings are immutable all the time 7 Lecturer: Hawraa Sh.

8 String Str = "Tutorials "; System.out.print("Found Index :" ); System.out.println(Str.indexOf( 'o' )); Found Index :4 String Str = "Welcome to Tutorialspoint.com"; System.out.print("Return Value :" ); System.out.println(Str.replace('o', 'T')); System.out.print("Return Value :" ); System.out.println(Str.replace('l', 'D')); Return Value :WelcTme tt TutTrialspTint.cTm Return Value :WeDcome to TutoriaDspoint.com String Str = "Welcome to Tutorialspoint.com"; System.out.print("Return Value :"); System.out.println(Str.toLowerCase()); Return Value :welcome to tutorialspoint.com String Str = new String("Welcome to Tutorialspoint.com"); System.out.print("Return Value :" ); System.out.println(Str.toUpperCase() ); Return Value :WELCOME TO TUTORIALSPOINT.COM 8 Lecturer: Hawraa Sh.

Appendix 3. Description: Syntax: Parameters: Return Value: Example: Java - String charat() Method

Appendix 3. Description: Syntax: Parameters: Return Value: Example: Java - String charat() Method Appendix 3 Java - String charat() Method This method returns the character located at the String's specified index. The string indexes start from zero. public char charat(int index) index -- Index of the