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.

Download 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.

Post on 13-Jan-2016

213 views

Category:

Documents

0 download

TRANSCRIPT

  • Primitive TypesJava offers a number of primitive types eg.) int, short, long double, float charA 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.

  • charsThe char type can store one character value 'A', '\n', '\u00E9

    char represented by a 16 bit unsigned integer

    * A total of 216 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 2nd 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 NumbersConvert 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

Recommended

View more >