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Introduction to Strings and Reading Input in Java

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Learn about strings in Java, including creating, concatenating, and extracting parts of strings. Also, explore reading input from the keyboard using the Scanner class.

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Introduction to Strings and Reading Input in Java

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  1. Week 6 Introduction to Computer Science and Object-Oriented Programming COMP 111 George Basham

  2. Week 6 Topics 6.1.1 Strings 6.1.2 Reading Input

  3. 6.1.1 Strings • A string is a series of characters such as “Hello, World!” • Strings are delimited by (enclosed within) quotation marks • Creating a string object does not require the new operator: String msg = “Hello, World!”; • The length of the example string above is 13 and can be determined via a call to the length method: System.out.println(msg.length());

  4. 6.1.1 Strings • The + operator is used to concatenate strings (put them together): String a = “Agent”; int n = 7; String bond = a + n; • Note that the integer value n is converted to a string • Use concatenation to simplify expressions: System.out.println(“Total is ” + total);

  5. 6.1.1 Strings • If a string contains digits of a number, you can use the Integer.parseInt or the Double.parseDouble method to obtain the number value • int count = Integer.parseInt(input); • double price = Double.parseDouble(input);

  6. 6.1.1 Strings • Use the substring method to extract a part of a string: s.substring(start, pastEnd) • You specify the position you want to start at, and the position one past the position you want to end at • String msg = “Hello, World!”; • String sub = msg.substring(0, 5); • // sub is “Hello”

  7. 6.1.1 Strings • String msg = “Hello, World!”; • String sub = msg.substring(7, 12); • // sub is “World” • String sub = msg.substring(7); // World! • Above copies from start pos to end

  8. 6.1.2 Reading Input • In Java version 5.0, a Scanner class was added that lets you read keyboard input in a convenient manner • To construct a Scanner object, simply pass the System.in object to the Scanner constructor: Scanner in = new Scanner(System.in); • Once you have a scanner, use nextInt or nextDouble method to read a whole number or a floating point number.

  9. 6.1.2 Reading Input • Scanner in = new Scanner(System.in); • System.out.print(“Enter Quantity: ”); • int quantity = in.nextInt(); • System.out.print(“Enter Price: ”); • double price = in.nextDouble();

  10. 6.1.2 Reading Input • nextLine() gets all text including spaces, next() gets a word (token) as soon as it comes to a white space (space, end of line, tab) • System.out.print(“Enter City: ”); • String city = in.nextLine(); • System.out.print(“Enter state code: ”); • String state = in.next();

  11. Reference: Big Java 2nd Edition by Cay Horstmann 6.1.1 Strings (section 4.6 in Big Java) 6.1.2 Reading Input (section 4.7 in Big Java)

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