04_strings.md

The following is from the Java tutorial

Tutorial

• What is a Class?
  • "In the real world, you'll often find many individual objects all of the same kind. There may be thousands of other bicycles in existence, all of the same make and model. Each bicycle was built from the same set of blueprints and therefore contains the same components. In object-oriented terms, we say that your bicycle is an instance of the class of objects known as bicycles. A class is the blueprint from which individual objects are created.""
• And an object is an instance of a class
• The following Bicycle class is one possible implementation of a bicycle:

class Bicycle {

    int cadence = 0;
    int speed = 0;
    int gear = 1;

    void changeCadence(int newValue) {
         cadence = newValue;
    }

    void changeGear(int newValue) {
         gear = newValue;
    }

    void speedUp(int increment) {
         speed = speed + increment;   
    }

    void applyBrakes(int decrement) {
         speed = speed - decrement;
    }

    void printStates() {
         System.out.println("cadence:" +
             cadence + " speed:" +
             speed + " gear:" + gear);
    }
}

Java String class

• A String is a sequence of characters
• In Java, Strings are objects or instances of the String class
• String literals in Java programs are implemented as instances of the String class such as

String s = “abcd”;

• This creates a new String object representing the string "abcd"
• Take a look at the Java documentation for String
• Java has numerous constructors for the String class
  • String(), construct a String representing the empty character sequence
  • String(byte[] bytes), construct a new String consisting of the bytes in the byte array bytes
  • String(char[] chars), construct a new String consisting of the characters of the character array chars
  • String("abcd")
  • There are plenty more
• Strings are immutable or constant, so any changes you make to an existing String will create a new String
• Strings can be shared, in theory there should be a single copy of any String in your program, but don't count on it if they are created dynamically during the running of the program. There is a separate memory area "String space" and the intern() method returns a shared copy that is put into the "String space"
• The class String also has numerous methods
• Getting a byte array for the bytes in the String
• Getting a char array for the characters in the String
• Changing the case
• Converting various primitive types to a String
• The "+" sign can be used for concatenation
• "abc" + "def" is the String "abcdef"
• StringBuilder and StringBuffer
• StringBuffer is thread safe and is a mutable sequence of characters
• StringBuilder is API compatible with StringBuffer, but it not thread safe
• Should be faster than StringBuffer in single-thread applications