1. F4105 JAVA PROGRAMMING
F4105 Java Programming
Introduction To Java Programming
1.0
Basic Concepts of Java Programming
2.0
Classes, Polymorphism and Inheritance
3.0
Exception handling
4.0

2. 3.0 CLASS, POLYMORPHISM AND INHERITANCE
3.4 String

3. LEARNING OUTCOMES TOPIC 3.4
F4105 JAVA PROGRAMMING
By the end of this chapter students shall be able to :
Declare and manipulate data of char type. 1
Explain String references as parameters 2
Differentiate between the String and StringBuffer class. 3
Construct programme using method in class String 4

4. Introduction A string is a sequence of characters.
F4105 JAVAPROGRAMMING
Introduction
A string is a sequence of characters.

5. String Declaration Example 1 char str [ ] = {'a','e','i','o','u'};
F4105 JAVAPROGRAMMING
String Declaration
Example 1
char str [ ] = {'a','e','i','o','u'};

6. String Declaration Example 2
F4105 JAVAPROGRAMMING
String Declaration
Example 2
char text[ ] = {'I','','C','A','N','','W','R','I','T', 'E','A','','G','O','O','D','','P','R','O','G','R','A','M','I','N','','J','A','V','A'};
Example 3
String text = "I CAN WRITE A GOOD PROGRAM IN JAVA";

7. class String class StringBuffer
F4105 JAVAPROGRAMMING
java.lang Package
class String class StringBuffer
method method

8. String Class String class is present in java.lang package.
F4105 JAVAPROGRAMMING
String Class
String class is present in java.lang package.
The methods in this class are used to manipulate strings.
The string objects created in a String class cannot be changed.
Example:
String obj = new String("Welcome");
obj.append("_World");
System.out.println(obj);
wrong

9. Creating String Object
F4105 JAVAPROGRAMMING
Creating String Object
Example 1:
Syntax
String stringobject = new String( );
Example:
String s=new String(“Java”);

10. Creating String Object
F4105 JAVAPROGRAMMING
Creating String Object
Example 2
Syntax
String stringobject = <string value>;
Example:
String s = "I have to study for my exams";

11. Creating String Object
F4105 JAVAPROGRAMMING
Creating String Object
Example 3
Syntax
String stringobject = new String(array_name);
Example:
char arr[ ] = {'H','E','L','L','O'};
String s = new String(arr);

12. Creating String Object
F4105 JAVAPROGRAMMING
Creating String Object
Example 4
Syntax
String stringobject = new String(stringobject);
Example:
char arr[ ] = {'H','E','L','L','O'};
String s = new String(arr);
String s1 = new String(s);

13. F4105 JAVAPROGRAMMING
String Methods
The String class has several methods that can be used to manipulate the string values.
Each method has its own characteristic.

14. length() method Is used to find the number of characters in a string.
F4105 JAVAPROGRAMMING
length() method
Is used to find the number of characters in a string.

15. length() method Example 1 String s = "I am going to school";
F4105 JAVAPROGRAMMING
length() method
Example 1
String s = "I am going to school";
int numchar = s.length( );
System.out.println(numchar);
Output 20

16. length() method Example 2 String s = " "; int numchar = s.length( );
F4105 JAVAPROGRAMMING
length() method
Example 2
String s = " ";
int numchar = s.length( );
System.out.println(numchar);
Output 2

17. length() method Syntax int variable_name = stringobject.length( );
F4105 JAVAPROGRAMMING
length() method
Syntax
int variable_name = stringobject.length( );

18. concat() method Example 1 String firststring = "The Twin Tower";
F4105 JAVAPROGRAMMING
concat() method
Example 1
String firststring = "The Twin Tower";
String secondstring = " looks beautiful";
String thirdstring = firststring.concat(secondstring); @
firststring+secondstring
Output
The Twin Tower looks beautiful

19. concat() method Syntax
F4105 JAVAPROGRAMMING
concat() method
Syntax
String Stringvariable3 = stringvariable1.concat (stringvariable2);

20. concat() method Example 2 String s1 = "Result: "+5+1;
F4105 JAVAPROGRAMMING
concat() method
Example 2
String s1 = "Result: "+5+1;
System.out.println(s1);
Output
Result: 51

21. concat() method Example 3 String s2 = "Result: "+(5+1);
F4105 JAVAPROGRAMMING
concat() method
Example 3
String s2 = "Result: "+(5+1);
System.out.println(s2);
Output
Result: 6

22. charAt() method Extracts a single character from a string
F4105 JAVAPROGRAMMING
charAt() method
Extracts a single character from a string

23. charAt() method Example String s = "Malaysia" char ch = s.charAt(4);
F4105 JAVAPROGRAMMING
charAt() method
Example
String s = "Malaysia"
char ch = s.charAt(4);
System.out.println(ch);
Output y

24. charAt() method Syntax
F4105 JAVAPROGRAMMING
charAt() method
Syntax
char variablename = stringobject.charAt(int where);

25. equals() method Compares two strings for equality.
F4105 JAVAPROGRAMMING
equals() method
Compares two strings for equality.

26. equals() method Example String s1="Both are equal";
F4105 JAVAPROGRAMMING
equals() method
Example
String s1="Both are equal";
String s2="Both are equal";
String s3="Both are not equal";
System.out.println(s1.equals(s2));
System.out.println(s1.equals(s3));
Output
true
false

27. equals() method Syntax
F4105 JAVAPROGRAMMING
equals() method
Syntax
boolean variablename = stringobject.equals(stringobject);

28. F4105 JAVAPROGRAMMING
indexOf() method
Will search the first occurrence of a character or set of characters inside a string.

29. indexOf() method Example 1 int val1 = s.indexOf('s');
F4105 JAVAPROGRAMMING
indexOf() method
Example 1
int val1 = s.indexOf('s');
System.out.println(val1);
Output 3

30. indexOf() method Example 2 int val2 = s.indexOf("is");
F4105 JAVAPROGRAMMING
indexOf() method
Example 2
int val2 = s.indexOf("is");
System.out.println(val2);
Output 2

31. indexOf() method Syntax
F4105 JAVAPROGRAMMING
indexOf() method
Syntax
int variablename = stringobject.indexOf(character);
int variablename = stringobject.indexOf(string);

32. F4105 JAVAPROGRAMMING
lastIndexOf() method
Will search the last occurrence of a character or a set of characters inside a string.

33. lastIndexOf() method Example 1 int val1 = s.lastIndexOf('s');
F4105 JAVAPROGRAMMING
lastIndexOf() method
Example 1
int val1 = s.lastIndexOf('s');
System.out.println(val1);
Output 12

34. lastIndexOf() method Example 2 int val2 = s.lastIndexOf("is");
F4105 JAVAPROGRAMMING
lastIndexOf() method
Example 2
int val2 = s.lastIndexOf("is");
System.out.println(val1);
Output 5

35. lastIndexOf() method Syntax
F4105 JAVAPROGRAMMING
lastIndexOf() method
Syntax
int variablename = stringobject.lastIndexOf(character);
int variablename = stringobject.lastIndexOf(string);

36. F4105 JAVAPROGRAMMING
replace() method
Will replace all occurrences of a character in a string with another character.

37. replace() method Example String s="Hewwo";
F4105 JAVAPROGRAMMING
replace() method
Example
String s="Hewwo";
String s1 = s.replace('w','l');
System.out.println(“Old string= “ + s);
System.out.println(“New string= “ + s1);
Output
Hewwo
Hello

38. replace() method Syntax
F4105 JAVAPROGRAMMING
replace() method
Syntax
String stringvariable = stringobject.replace(original,replacement);

39. F4105 JAVAPROGRAMMING
trim() method
Will trim the leading and trailing white spaces in a string.

40. trim() method Example String s=" Hello Malaysia ";
F4105 JAVAPROGRAMMING
trim() method
Example
String s=" Hello Malaysia ";
String s1 = s.trim( );
System.out.println(s1);
Output
Hello Malaysia

41. trim() method Syntax String stringvariable = stringobject.trim( );
F4105 JAVAPROGRAMMING
trim() method
Syntax
String stringvariable = stringobject.trim( );

42. F4105 JAVAPROGRAMMING
toLowerCase() method
Converts all the characters in a string from uppercase to lowercase.

43. toLowerCase() method Example String s1="LOWER";
F4105 JAVAPROGRAMMING
toLowerCase() method
Example
String s1="LOWER";
String s2 = s1.toLowerCase( );
System.out.println(s2);
Output
lower

44. toLowerCase() method Syntax
F4105 JAVAPROGRAMMING
toLowerCase() method
Syntax
String stringvariable = stringobject.toLowerCase( );

45. F4105 JAVAPROGRAMMING
toUpperCase() method
Converts all the characters in a string from lowercase to uppercase.

46. toUpperCase() method Example String s1="upper";
F4105 JAVAPROGRAMMING
toUpperCase() method
Example
String s1="upper";
String s2 = s1.toUpperCase( );
System.out.println(s2);
Output
UPPER

47. toUpperCase() method Syntax
F4105 JAVAPROGRAMMING
toUpperCase() method
Syntax
String stringvariable = stringobject.toUpperCase( );

48. substring() method Extracts a part of the string.
F4105 JAVAPROGRAMMING
substring() method
Extracts a part of the string.

49. substring() method Example String s1="I do shopping in Mega Mall";
F4105 JAVAPROGRAMMING
substring() method
Example
String s1="I do shopping in Mega Mall";
String s2 = s1.substring(5,12);
System.out.println(s2);
Akrasa ke (5) sehingga aksara ke(12-1)
Output
shoppin

50. StringBuffer Class
Is a special class supported by Java to handle strings.
StringBuffer creates strings of flexible length whereas String class creates strings of fixed length.

51. Creating StringBuffer Objects
Example 1
StringBuffer sb1 = new StringBuffer();
Syntax
StringBuffer StringBufferobject = new StringBuffer();

52. Creating StringBuffer Objects
Example 2
StringBuffer s = new StringBuffer(6);
Syntax
StringBuffer StringBufferobject = new StringBuffer(integervariable);

53. Creating StringBuffer Objects
Example 3
StringBuffer sb3 = new StringBuffer ("Java");
Syntax
StringBuffer StringBufferobject = new StringBuffer(stringvariable);

54. length() method
Finds the current length of a StringBuffer object.

55. length() method Example StringBuffer sb1 = new StringBuffer(“Java”);
System.out.println (sb1.length());
Output 4

56. capacity() method
Returns the amount of memory allocated for the StringBuffer object.

57. capacity() method Example Output 30
StringBuffer sb = new StringBuffer("Capacity of sb");
System.out.println (sb.capacity());
* “Capacity of sb” = (free storage) = 30 (amount of storage)
Output 30

58. capacity() method Example Output 16
StringBuffer sb1 = new StringBuffer("");
System.out.println (sb1.capacity());
* “Capacity of sb” = 16(free storage) = 16 (amount of storage)
Output 16

59. append() method
Allows data to be added to the end of a StringBuffer object.

60. append() method Example
StringBuffer sb1 = new StringBuffer("Welcome to beautiful");
sb1.append("_World");
System.out.println(sb1);
Output
Welcome to beautiful_World

61. setCharAt() method
Sets the character at any position within a StringBuffer.

62. setCharAt() method Example
StringBuffer sb1 = new StringBuffer("Hello World");
sb1.setCharAt(5,'_');
System.out.println(sb1);
Output
Hello_World

63. insert() method
Allows data to be added at a specified position in the StringBuffer object.

64. insert() method Example
StringBuffer sb1 = new StringBuffer("Hello World");
sb1.insert(6,"Java ");
System.out.println(sb1);
Output
Hello Java World

65. reverse() method Example StringBuffer sb=new StringBuffer("roweT");
sb.reverse( );
System.out.println(sb);
Output
Tower

66. delete() method Example StringBuffer sb=new StringBuffer(“Program");
sb.delete(2, 5 ); //(2,(5-1))
System.out.print(sb);
Output
Pram

67. deleteCharAt() method
Example
StringBuffer sb=new StringBuffer(“Java");
sb.deleteCharAt(1 );
System.out.print(sb);
Output
Jva