1. Strings as objects Strings are objects. Each String is an instance of the class String They can be constructed thus: String s = new String("Hi mom!"); Strings are so common, Java provides a handier way of creating them: String s = "Hi mom!"; Strings have methods: loads of them!!!

2. Some methods for Strings String s1 = "harry"; String s2 = "harold"; if ( s1.equals(s2) ) System.out.println("Strings are the same"); if ( s1.compareTo(s2) < 0 ) System.out.println(s1 + "...." + s2); else System.out.println(s2 + "...." + s1);

3. Comparing Strings s1.compareTo("hi mom!") returns a value < 0 if this s1 is ordered before "hi mom" returns a value > 0 if "hi mom" is ordered before s1 returns 0 if they are the same Ordering is called lexicographic order

4. String concatenation String s1 = "Hi" + " mom"; String s2 = "your lucky number is " + number; String s3 = s1.concat(s2); String s3 = s1 + s2; A number will be first turned into a String, then concatenated.

5. Substrings A String is stored as an array of characters: Hi_Mom! 0123456index: character: public String substring(int beginIndex) public String substring(int beginIndex, int endIndex)

6. Other String methods return the character at a given index: –public char charAt(int index) get the length of a String: –public int length()

7. Processing string contents: Scanner All the strings we’ve seen before have been short (a word or two). To process long strings (such as sentences) we need to be able to split up strings into their parts (words, numbers, etc.). The parts of a sentence are called tokens. We can use the java.util.Scanner class to create Scanner objects which go through a string “scanning” for tokens. “This is a string with 9 tokens in it.” token How do we recognise tokens? They are separated by delimiters (in the sentence above, blank spaces).

8. Using a scanner object to read words from a string // start with Import java.util.Scanner; String s = “I know lots of words”; Scanner myScanner = new Scanner(s); int wordcount = 0; while(myScanner.hasNext()){ System.out.println(myScanner.next()); wordcount++; } System.out.println(wordcount+“ words in total”); Objects from the Scanner class hold a stream of input from some source, and scan the stream for the next string, int, line, etc To use a scanner, we first create a new scanner object and give it the thing we want it to scan. The new scanner object holds that source inside itself. We use methods inside that scanner object we created to get the next string: myScanner.next(), int: myScanner.nextInt() etc.

9. System.out and System.in System.out is a static object in the System class that links to output to the console. We can use methods contained in this out object to print things on the console: System.out.println(“hello!”); The System class also contains a static object System.in that links to input from the console. We can read input from System.in, but we must use a Scanner object to do it.

10. Using the scanner class to read System.in input from the console System.in has minimal set of features–it can only read one byte at a time In Java 5.0, the Scanner class was added to read input in a convenient manner nextDouble() reads a double nextLine() reads a line (until user hits Enter) next() reads a word (until any white space) Scanner in = new Scanner(System.in); System.out.print("Enter quantity: "); int quantity = in.nextInt();

11. Using a scanner object to read from input import java.util.Scanner; class testScanner{ public static void main(String[] args){ Scanner myScanner = new Scanner(System.in); System.out.print("Enter your name: "); String name = myScanner.next(); System.out.print("Enter your age: "); int age = myScanner.nextInt(); System.out.println("hello "+name+" ("+age+")"); } Objects from the Scanner class hold a stream of input from some source, and scan the stream for the next string, int, line, etc To use a scanner, we first create a new scanner object and give it the source stream we want it to scan. The new scanner object holds that source stream inside itself. We use the methods inside the scanner object we created to get the next string: myScanner.next(), int: myScanner.nextInt() etc.

12. Some methods in the Scanner class public Scanner(String x) –Constructs a new scanner object and gives it a String to scan. The newly created object will return words (or other tokens) out of that string. public Scanner(InputStream x) –Constructs a new scanner object and gives it a stream of input to scan. The new object will return words (or other tokens) out of that input stream. public Scanner(File x) –Constructs a new scanner object and gives it a File to scan. The newly created object will return words (or other tokens) out of that File. public String next() –Takes the next string (ending with a space) from x and returns it. public boolean hasNext() –Returns true if there is something left to read from the scanner public int nextInt() –Takes the next thing from stream x, converts it to an int, and returns it. public boolean hasNextInt() –Returns true if there is an int to read from the scanner public Double nextDouble() public String nextLine() public boolean hasNextDouble() public boolean hasNextLine()

13. Using scanner We can construct scanner objects to scan Strings, input from System.in, and files (we’ll learn about scanning files later). This is because the scanner class has different constructors for each of those types of input. Once we’ve created a scanner object for some input, we can get strings, ints, doubles, or whole lines from that object, using the relevant scanner methods on that object. We can also check, before we get any of those, whether there is actually a string, int, double or line to get (again, using the relevant “hasNext” methods). The best place to learn about scanner objects is on the Java api website. Go to http://java.sun.com/j2se/1.5.0/docs/api// and search for scanner in the “all classes” window on the lower left