Download String str="I Love Java"

PROGRAMMING 2 CS112- LAB 2
JAVA
TA: NOUF AL-HARBI
WWW.ACADOX.COM/CLASS/ 14347
[email protected]
LAB OBJECTIVES
The String Class Applications:
String.
Methods of the String Class.
Lab4_1, Programming 2
2
Exercises.
STRING
String is a sequence of characters enclosed in
quotes. E.g. “Hello”
Once a String object is created it cannot be
changed. Stings are Immutable.
To get changeable strings use the class called
StringBuffer.
Lab4_1, Programming 2
3
String and StringBuffer classes are declared
final, so there cannot be subclasses of these
classes.
HOW TO CREATE A STRING
String newString = new String(stringLiteral);
String s1= new String("Welcome to Java");
Since strings are used frequently, Java provides a
shorthand initializer for creating a string:
Lab4_1, Programming 2
4
String s1= "Welcome to Java";
STRINGS ARE IMMUTABLE
A String object is immutable: its content cannot be
changed.
Does the following code changes the content of the
string?
String s = "Java";
Lab4_1, Programming 2
5
s = "HTML";
TRACE CODE
String s = "Java";
s = "HTML";
After executing s = "HTML";
After executing String s = "Java";
s
: String
String object for "Java"
Contents cannot be changed
s
: String
This string object is
now unreferenced
String object for "Java"
: String
Lab4_1, Programming 2
6
String object for "HTML"
ANOTHER EXAMPLE OF
IMMUTABILITY
String str1 = “Hello”;
String str2 = “Hello”;
Lab4_1, Programming 2
√
7
Χ
INTERNED STRINGS
Since strings are immutable and are frequently used, to
improve efficiency and save memory, the JVM uses a
unique instance for string literals with the same
character sequence.
Such an instance is called interned.
Lab4_1, Programming 2
8
For example, the following statements:
EXAMPLES
String s1 = "Welcome to Java";
String s2 = new String("Welcome to Java");
s1
s3
: String
Interned string object for
"Welcome to Java"
String s3 = "Welcome to Java";
System.out.println("s1 == s2 is " + (s1 == s2)); s2
System.out.println("s1 == s3 is " + (s1 == s3));
: String
A string object for
"Welcome to Java"
• A new object is created if you use the
Lab4_1, Programming 2
9
s1 == s2 is false
s1 == s3 is true
new operator.
• If you use the string initializer, no new
object is created if the interned object is
already created.
STRING/CHARACTER METHODS
String str="I Love Java";
String str1= "I Love Java";
String str2=" Programm ";
char charAt(int index)
Lab4_1, Programming 2
Description
Returns the character at
the specified index.
Example
char x=str.charAt(2);
10
Method
STRING/CHARACTER
METHODS
String str="I Love Java";
String str1= "I Love Java";
String str2=" Programm ";
Description
int compareTo(String
s)
int
compareToIngoreCase
(s)
Compares this
String to another
Object or String.
returns +ve
number, 0, or -ve
number if this
String is greater
than, equal to or
less than s.
Lab4_1, Programming 2
Example
int comp=str.compareTo(str2);
int comp2=str.compareToIngoreCase (str2);
11
Method
STRING/CHARACTER
METHODS
String str="I Love Java";
String str1= "I Love Java";
String str2=" Programm ";
String concat(String
str)
Lab4_1, Programming 2
Description
Concatenates the specified
string to the end of this
string.
Example
String str2=" Programm ";
String res=str.concat(str2);
12
Method
STRING/CHARACTER
METHODS
String str="I Love Java";
String str1= "I Love Java";
String str2=" Programm ";
Description
Example
boolean equals(Object
anObject)
Compares this string to
the specified object.
returns true if s the same
as this String.
boolean isEqual=str.equals(str);
Lab4_1, Programming 2
13
Method
STRING/CHARACTER
METHODS
String str="I Love Java";
String str1= "I Love Java";
String str2=" Programm ";
int length()
Lab4_1, Programming 2
Description
Returns the length of this
string.
Example
int len=str.length();
14
Method
STRING/CHARACTER
METHODS
String str="I Love Java";
String str1= "I Love Java";
String str2=" Programm ";
String substring(int
beginIndex)
Lab4_1, Programming 2
Description
Returns a new string that is
a substring of this string.
Example
String res1=str.substring(2);
15
Method
STRING/CHARACTER
METHODS
String str="I Love Java";
String str1= "I Love Java";
String str2=" Programm ";
Description
Example
String substring(int
beginIndex, int
endIndex)
Returns a new string that is
a substring of this string.
String res1=str.substring(2,6);
String substring(int
beginIndex, int
endIndex)
Returns a new string that is
a substring of this string.
String res1=str.substring(2,6);
Lab4_1, Programming 2
16
Method
STRING/CHARACTER
METHODS
String str="I Love Java";
String str1= "I Love Java";
String str2=" Programm ";
String toUpperCase()
String toLowerCase()
Lab4_1, Programming 2
Description
returns a new String,
equivalent to the
Upper/lower case of this
String
Example
String upCase=str.toUpperCase();
String lowCase=str.toLowerCase();
17
Method
STRING/CHARACTER
METHODS
String str="I Love Java";
String str1= "I Love Java";
String str2=" Programm ";
Description
Character.isLetter(char determines if
ch)
the specified
character is a
letter.
Lab4_1, Programming 2
Example
boolean isLetter=Character.isLetter('r');
Ex2:
boolean
isLetter=Character.isLetter(str.charAt(5));
18
Method
Description
char charAt(int index)
Returns the character at the specified index.
int compareTo(String s)
int
compareToIngoreCase(s)
Compares this String to another Object or String.
returns +ve number, 0, or -ve number if this String is
greater than, equal to or less than s.
String concat(String str)
Concatenates the specified string to the end of this
string.
boolean equals(Object
anObject)
Compares this string to the specified object.
returns true if s the same as this String.
int length()
Returns the length of this string.
String substring(int
beginIndex)
Returns a new string that is a substring of this string.
String substring(int
beginIndex, int endIndex)
Returns a new string that is a substring of this string.
Character.isLetter(char ch)
determines if the specified character is a letter.
String toUpperCase()
String toLowerCase()
returns a new String, equivalent to the Upper/lower
case of this String
Lab4_1, Programming 2
19
Method
Example of String Operations
Design and implement a Java program that will do the
following operations to this string s1=“Welcome to java”
s2=“Welcome to Java”
1. Print out the length of the string.
2. Use concat method which concatenates s1 to s2.
3. Use CharAt method which returns the character of s1 at
index 1
4. Convert all s1 alphabets to capital letters and print out the
result.
5. Convert all s1 alphabets to lower-case letters and print out
the result.
Lab4_1, Programming 2
20
 Using methods of the String Class.
Example of String Operations
Lab4_1, Programming 2
21
6. Use equals method which compare s1 to s2.
7.Use equalsIgnoreCase method which compare s1 to s2
ignoring case consideration.
8. Use CompareTo method which compare s1 to s2.
9. Use Substring method which extracting substring from s1.
Lab4_1, Programming 2
22
Constructing two
strings
Lab4_1, Programming 2
23
Using Length
method which
returns the length
of s1
Lab4_1, Programming 2
24
Using concat method
which concatenates s1
to s2
Lab4_1, Programming 2
25
Using CharAt method
which returns the
character of s1 at index
1
Lab4_1, Programming 2
26
Using
toUpperCase
method which
converts all the
character of s1
to uppercase
Lab4_1, Programming 2
27
Using toLowerCase
method which
converts all the
character of s1 to
lowercase
Lab4_1, Programming 2
28
Using equals
method which compare s1
to s2
Lab4_1, Programming 2
29
Using equalsIgnoreCase
method which compare s1
to s2 ignoring case
consideration
Lab4_1, Programming 2
30
Using CompareTo
method which
compare s1 to s2
Lab4_1, Programming 2
31
Using Substring
method which
extracting substring
from s1
Lab4_1, Programming 2
32
The Output
EXERCISE1: PHONE
KEYPADS
Problem Description:
Lab4_1, Programming 2
33
The international standard letter/number mapping
found on the telephone is shown below:
EXERCISE1: PHONE KEYPADS
Write a method that returns a number, given an
uppercase letter, as follows:
public static int getNumber(char uppercaseLetter)
Lab4_1, Programming 2
34
Write a test program that prompts the user to enter a
phone number as a string. The input number may
contain letters. The program translates a letter (upperor lowercase) to a digit and leaves all other characters
intact.
Lab4_1, Programming 2
35
OUTPUT
Any question
Lab4_1, Programming 2
36
THANK YOU