Primitive Types Java offers a number of primitive types eg.) int, short, long double, float char A variable which is declared as a primitive type stores any value assigned to it. A variable which is declared as a class type can store the reference to an object of that type.

chars The char type can store one character value 'A', '\n', '\u00E9‘ char represented by a 16 bit unsigned integer * A total of 2 16 different Unicode chars can be represented int value; char letter; value = 5; letter = ‘5’; value = letter; //stores a 53 letter = value; //error ……. Information can be lost // when converting 32 bits to 16

A String is NOT a primitive type.. String is a class provided by the Java API (A object of this type stores a ordered group of chars) Strings ARE OBJECTS!! Look at Java API specs………….

The String class provides constructors String word; word = new String(“hello”); //constructing a //String object from a String literal Seems redundant …. String is the ONLY class that lets you create a String object by assigning a value…. word = “hello”;

String constructors are useful, however String word, word2; word = JOptionPane.showInputDialog(“Enter info:”); The showInputDIalog method calls one of the String constructors to create a String object. This String object is then returned to the caller. word2 = new String(word); You would call a constructor to make a copy of an existing String.

int length() length() method returns the number of chars in a String object System.out.println(“size” + “hello”.length()) ; The length of a String is not always obvious… String in = JOptionPane.showInputDialog(“Enter”); int size = in.length();

String characters are indexed………… The first character in a String is at index 0. Note: last char is at index: length()-1

char charAt(int) charAt method returns character from a string the String object is unchanged by this call String in = JOptionPane.showInputDialog(“Enter”); JOptionPane.showMessageDialog(null,”first char is” + in.charAt(0) ); JOptionPane.showMessageDialog(null,”last char is” + in.charAt(in.length()-1 ) );

String substring(int,int) This method returns a new String object, which contains a portion of the characters of the invoking object Parameters supply start and “past the end” position String in, apiece; in = JOptionPane.showInputDialog(“Enter”); //user types hello world apiece = in.substring(1,8); // String in is unchanged // String apiece contains characters “ello wo”

A String is an IMMUTABLE object………… Note that we changed the String object that in was referring to by creating a new object and assigning the new object to in. It is not possible to change the data (chars) stored in a String object. If you wish to do this, you must create a new String object. This is because the String class has no mutator methods (methods which change its instance data). A class without mutator methods is called IMMUTABLE.

int indexOf(char) indexOf method returns the position of the first occurrence of parameter (-1 if parameter does not occur) String in = JOptionPane.showInputDialog(“Enter”); int blk = in.indexOf(“ “); //where is first blank? If user had entered hello world, blk now contains 5 in = in.substring(blk+1, in.length() ); //in is now referencing an object without the first word

String substring(int) Many String methods are OVERLOADED … This call has an implied 2 nd parameter – which is the length of the String String in = JOptionPane.showInputDialog(“Enter”); int blk = in.indexOf(“ “); //where is first blank? If user had entered hello world, blk now contains 5 in = in.substring(blk+1 ); //in is now referencing an object without the first word

+ is the String concatenation operator + is an overloaded operator in Java String fname = "Harry"; String lname = "Hacker"; String name = fname + lname; name is "HarryHacker" If one operand of + is a string, the other is converted to a string: String a = "Agent"; String name = a + 7; name is "Agent7" You commonly use this for output: System.out.println(“The value is “ + 7 );

Converting between Strings and Numbers Convert to number: int n = Integer.parseInt(str); double x = Double.parseDouble(x); Convert to string: String str = Integer.toString(n); More efficient, less readable str = "" + n; System.out.println(“” + n ); //explicit conversion needed here

Practice Convert String word to pig latin (assume word stores 1 word) Ask user for a a sentence If the word COW is contained in the sentence, replace the first occurrence of it with MOOSE Replace ALL occurrances of COW with MOOSE