Embed Size (px)
Citation preview
10/21/10 1
10/21/10 2
What are Strings? . . .
• A combination of characters is a string.
• Strings are instances of the class ‘String’.
• When a string is used in programs, JAVA automatically creates instances of the String class.
10/21/10 3
Declaring string variables . . .
String variable_name;
When the values are assigned to string variables, the value should be given within the double quotations (“ “).
Ex:String name=“Kamal”;String empNo=“EMP102”;String address=“No:5,Pushpadana Mawatha, Kandy”;
02/10/10 4
Example 1. . .
class String_Example{
public static void main(String arg[]) {
;”String f_name=“Malan;”String m_initial=“C;”String l_name=“Karunarathne
;System.out.println(f_name+” “+m_initial+” “+l_name) {
{
class String_Example{
public static void main(String arg[]) {
String f_name=“Malan”;String m_initial=“C”;String l_name=“Karunarathne”;
System.out.println(f_name+” “+m_initial+” “+l_name); {
{
Write a simple JAVA program that prints the full name, when the first name, middle initial and the last name is given.
10/21/10 5
String constructors . . .
• String class contains a default constructor with no parameters .
• It creates an empty string.
String s=new String();
10/21/10 6
String constructors (cont) . . .
• To create a String initialized with characters, we can call another constructor of String class that accepts a char array.
char arr[]={‘a’ , ’b’ , ’c’, ’d’ , ’e’ };
String s=new String(arr);
10/21/10 7
String constructors (cont) . . .
• There is another constructor in String class, that allows to specify the starting index and the number of characters to be included as the new string value.
char arr[]={‘a’ , ’b’ , ’c’, ’d’ , ’e’ };
String s=new String(arr,2,3);
This indicates that s contains 3 characters starting from index 2.
10/21/10 8
String Arithmetic . . .
• The ‘+’ sign does not mean “addition” when it is used with String objects. In other words, the ‘+’ sign, behave differently when it is used with Strings.
It represents
“Concatenate two strings”
The ‘+’ sign creates a single String that contains the concatenation its operands.
02/10/10 9
Example 2. . .
class String_Example{
public static void main(String arg[]) {
;”String f_name=“Malan;”String m_initial=“C;”String l_name=“Karunarathne
+String full_name=f_name” “+m_initial+” “ l_name+;
;System.out.println(full_name) {
{
class String_Example{
public static void main(String arg[]) {
String f_name=“Malan”;String m_initial=“C”;String l_name=“Karunarathne”;
String full_name=f_name+“ ”+m_initial+“ ” +l_name;
System.out.println(full_name); {
{
10/21/10 10
String Arithmetic (cont). . .
• Add numerical values to a String…Ex:
int num=45; String code=“EMP” + 45;
The compiler calls a method that turns the numerical values into a String, which can be added with the + sign.
• The operator += can be used with the String.Ex:
String fname=“Kamal”;fname=fname+”Perera”;
orfname+=“Perera”;
10/21/10 11
String Methods . . .The String class provides number of methods to manipulate Strings.
Method Use
length() Number of characters in a String
charAt() The Character at the specified location in the String
toCharArray() Produce a char[] containing the characters in the String
equals() An equality check on the contents of the two Strings. Consider the case (Upper case & Lower case) of the characters.
equalsIgnoreCase() An equality check on the contents of the two Strings. The case of the characters are ignored.
10/21/10 12
String Methods (Cont) . . .Method Use
compareTo() Result is negative, zero or Positive depending on the lexicographical ordering of the Strings and the argument. Uppercase & Lowercase are not equal
indexOf() Returns -1 if the argument is not found within the String. Otherwise returns the index where the argument starts.
lastIndexOf() Similar to the indexOf(). But searching starts from the back end of the String.
substring() Returns a new String object containing the specified character list.
concat() Returns a new String object containing the original String’s characters followed by the characters in the argument.
10/21/10 13
String Methods (Cont) . . .
Method Use
toLowerCase() Returns a new String by converting all the characters of the String to the lower case letters.
toUpperCase() Returns a new String by converting all the characters of the String to the upper case letters.
10/21/10 14
String Methods: Examples . . .
Ex (1): Find the length of Text
int length=address.length();int length=address.length();
Consider the following text.
String address=“32/A, Passara road, Badulla”;
Ex (2): Find the character in the 3th index
char ch=address.charAt(3);char ch=address.charAt(3);
10/21/10 15
String Methods: Examples (Cont). . .
Ex (4): Find the index of last ‘,’
int index_comma=address.lastIndexOf(‘,’);int index_comma=address.lastIndexOf(‘,’);
Ex (5): Extract the street of the address (ie. Passara road)
String street=address.substring(6,index_comma);String street=address.substring(6,index_comma);
Ex (3): Find the index of Text ‘/’
int index_slash=address.indexOf(‘/’);int index_slash=address.indexOf(‘/’);
10/21/10 16
String Methods: Examples (Cont). . .
Ex (7): Convert the address to lower case letters
String lower_case=address.toLowerCase();String lower_case=address.toLowerCase();
Ex (6): Convert the address to upper case letters
String upper_case=address.toUpperCase();String upper_case=address.toUpperCase();
10/21/10 17
Command Line Arguments . . .
• JAVA enables to get different kinds of inputs by passing as command line arguments.
• Command line arguments are given when the JAVA program is run.
• The JAVA program stores the command line arguments in the array of Strings which is passed to the main method in the program.
public static void main(String arg[]){
}
10/21/10 18
Command Line Arguments (Cont) . . .
Apple Orange Lime
public static void main(String arg[]){
}
10/21/10 19
Command Line Arguments (Cont) . . .
Apple Orange Lime
arg[0] arg[1] arg[2]
Number of arguments given in the command line (length of the String array) is given by,
arg.length
10/21/10 20
Example . . .
public static void main(String arg[]){
for(int i=0;i<arg.length;i++){
;System.out.println(arg[i])
{{
public static void main(String arg[]){
for(int i=0;i<arg.length;i++){
System.out.println(arg[i]);
{{
10/21/10 21
Command Line Arguments (Cont) . . .
• All the arguments which are passed to the main method are considered as Strings. In order to treat them as non-Strings, they should be converted into specific type.
These Strings should be converted to integer values
10/21/10 22
Converting Strings to Numerical values . . .
• Converting Strings to integer values.String num=“34”;int n=Integer.parseInt(num);
• Converting Strings to float values.String num=“34.78”;float n=Float.parseFloat(num);
•Converting Strings to float values.String num=“34.98”;double n=Double.parseDouble(num);
