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Programming 2 CS112- Lab 2 Java

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Presentation on theme: "Programming 2 CS112- Lab 2 Java"— Presentation transcript:

1 Programming 2 CS112- Lab 2 Java
TA: Nouf Al-Harbi

2 Lab Objectives The String Class Applications: String.
Methods of the String Class. Exercises. Lab4_1, Programming 2

3 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. String and StringBuffer classes are declared final, so there cannot be subclasses of these classes. Lab4_1, Programming 2

4 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: String s1= "Welcome to Java"; Lab4_1, Programming 2

5 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"; s = "HTML"; Lab4_1, Programming 2

6 Trace Code String s = "Java"; s = "HTML"; Lab4_1, Programming 2

7 Another Example of Immutability
String str1 = “Hello”; String str2 = “Hello”; Χ √ Lab4_1, Programming 2

8 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. For example, the following statements: Lab4_1, Programming 2

9 s1 == s2 is false s1 == s3 is true
Examples s1 == s2 is false s1 == s3 is true A new object is created if you use the new operator. If you use the string initializer, no new object is created if the interned object is already created. Lab4_1, Programming 2

10 String/Character Methods
String str="I Love Java"; String str1= "I Love Java"; String str2=" Programm "; Example Description Method char x=str.charAt(2); Returns the character at the specified index. char charAt(int index) Lab4_1, Programming 2

11 String/Character Methods
String str="I Love Java"; String str1= "I Love Java"; String str2=" Programm "; Example Description Method int comp=str.compareTo(str2); int comp2=str.compareToIngoreCase (str2); 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. int compareTo(String s) int compareToIngoreCase(s) Lab4_1, Programming 2

12 String/Character Methods
String str="I Love Java"; String str1= "I Love Java"; String str2=" Programm "; Example Description Method String str2=" Programm "; String res=str.concat(str2); Concatenates the specified string to the end of this string. String concat(String str) Lab4_1, Programming 2

13 String/Character Methods
String str="I Love Java"; String str1= "I Love Java"; String str2=" Programm "; Example Description Method boolean isEqual=str.equals(str); Compares this string to the specified object. returns true if s the same as this String. boolean equals(Object anObject) Lab4_1, Programming 2

14 String/Character Methods
String str="I Love Java"; String str1= "I Love Java"; String str2=" Programm "; Example Description Method int len=str.length(); Returns the length of this string. int length() Lab4_1, Programming 2

15 String/Character Methods
String str="I Love Java"; String str1= "I Love Java"; String str2=" Programm "; Example Description Method String res1=str.substring(2); Returns a new string that is a substring of this string. String substring(int beginIndex) Lab4_1, Programming 2

16 String/Character Methods
String str="I Love Java"; String str1= "I Love Java"; String str2=" Programm "; Example Description Method String res1=str.substring(2,6); Returns a new string that is a substring of this string. String substring(int beginIndex, int endIndex) Lab4_1, Programming 2

17 String/Character Methods
String str="I Love Java"; String str1= "I Love Java"; String str2=" Programm "; Example Description Method String upCase=str.toUpperCase(); String lowCase=str.toLowerCase(); returns a new String, equivalent to the Upper/lower case of this String String toUpperCase() String toLowerCase() Lab4_1, Programming 2

18 String/Character Methods
String str="I Love Java"; String str1= "I Love Java"; String str2=" Programm "; Example Description Method boolean isLetter=Character.isLetter('r'); Ex2: boolean isLetter=Character.isLetter(str.charAt(5)); determines if the specified character is a letter. Character.isLetter(char ch) Lab4_1, Programming 2

19 Returns the character at the specified index. char charAt(int index)
Description Method Returns the character at the specified index. char charAt(int index) 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. int compareTo(String s) int compareToIngoreCase(s) Concatenates the specified string to the end of this string. String concat(String str) Compares this string to the specified object. returns true if s the same as this String. boolean equals(Object anObject) Returns the length of this string. int length() Returns a new string that is a substring of this string. String substring(int beginIndex) String substring(int beginIndex, int endIndex) determines if the specified character is a letter. Character.isLetter(char ch) returns a new String, equivalent to the Upper/lower case of this String String toUpperCase() String toLowerCase() Lab4_1, Programming 2

20 Example of String Operations
Using methods of the String Class. Design and implement a Java program that will do the following operations to this string s1=“Welcome to java” s2=“Welcome to Java” Print out the length of the string. Use concat method which concatenates s1 to s2. Use CharAt method which returns the character of s1 at index 1 Convert all s1 alphabets to capital letters and print out the result. Convert all s1 alphabets to lower-case letters and print out the result. Lab4_1, Programming 2

21 Example of String Operations
Use equals method which compare s1 to s2. Use equalsIgnoreCase method which compare s1 to s2 ignoring case consideration. Use CompareTo method which compare s1 to s2. 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 method which compare s1 to s2
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 method which compare s1 to s2
Using CompareTo method which compare s1 to s2 Lab4_1, Programming 2

31 method which extracting substring from s1
Using Substring method which extracting substring from s1 Lab4_1, Programming 2

32 The Output Lab4_1, Programming 2

33 Exercise1: Phone keypads
Problem Description: The international standard letter/number mapping found on the telephone is shown below: Lab4_1, Programming 2

34 Exercise1: Phone keypads
Write a method that returns a number, given an uppercase letter, as follows: public static int getNumber(char uppercaseLetter) 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 (upper- or lowercase) to a digit and leaves all other characters intact. Lab4_1, Programming 2

35 Output Lab4_1, Programming 2

36 Any question Thank you Lab4_1, Programming 2

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