Chapter 8 String

1. Chapter 8 String Lecturer: Ty Rasmey Email: rasmeyt2@gmail.com

2. Overview • Introduction • The String Class • The Character Class • The StringBuffer Class

3. Introduction • A string is sequence of characters. • A string is not an array of character • E.g. in C/C++: char s[10]; • In Java, A String is an object. • Java has 3 String classes: • String • Character • StringBuffer

4. The String Class

5. The String Class • String is in java.lang package. • Since java.lang.*is always imported automatically, we don’t need to import the Stringclass. • Declaration: String s1; • Initialization: s1=“Welcome to Java”; • Or, short-cut: String s1=“Welcome to Java”;

6. The String class(2) • Because String is a class, then s1 is an object. • So there should be constructors, methods, or properties. • String constructors: • String() • String(String value) • String(char[] value) Ex: String s1 = new String(“npic”); • Since strings are used frequently, Java treats a string literal as a String object. So can say: • String s1 = “npic”;

7. The String class(3) Summary of String class • Constructors • String() • String(value: String) • String(value: char[]) • Methods • charAt() • compareTo() • concat() • endsWidth() • equals() • getChars() • equalsIgnoreCase() • getChars() • indexOf() • lastIndexOf() • regionMatches() • length() • replace() • startsWith() • subString() • toCharArray() • toLowerCase() • toString() • toUpperCase() • trim() • copyValueOf() • valueOf()

8. The String class(4) • Q. How do I get those methods to use? • A. You just declare a variable as String. String s1=“Welcome to NPIC”; Then, you call a method, say length() & substring(intbeginIndex, intendIdex). • Let’s try this out: Public class TestString { public static void main(String[] args){ String s1=“Welcome to NPIC”; System.out.println(s1.length()); System.out.println(s1.substring(0,11) + “Java”); } }

9. The String class(5) Note: • The String class is immutable (has no setter method). • The String class is final so we cannot inherit from it. //Discuss it in chapter 9 • Lab time: • 8.2.11 Example: Checking Palindromes p.270

10. The Character Class

11. The Character class • To declare a variable as a character, use primitive data type: char. Ex: char ch1 = ‘a’; • But Java provides also Character class. It is useful for Data Structure. Ex: Character ch2 = new Character(‘b’); Character ch3 = ‘c’; • After define ch2,ch3 as Character, then these can use methods from Character class. Please see methods on section 8.3 page 271. • Lab Time: • 8.3.1 Example on page 272

12. The StringBuffer Class

13. The StringBuffer class • StringBuffer class is more flexible than String class. Why? • Because after creating a variable from StringBuffer class, we can use add, append, delete, insert etc. very easily. • Example: StringBuffersb = new StringBuffer(“Welcom”); sb.append(“e”);

14. The StringBuffer class(2) • StringBuffer() • append():StringBuffer • capacity():int • charAt():char • delete():StringBuffer • deleteCharAt():StringBuffer • insert():StringBuffer • length():int • replace():StringBuffer • reverse():StringBuffer • setCharAt():void • setLength():void • subString():String Homework

15. The StringBuffer class(3) • Append StringBufferst = new StringBuffer(“Welcome"); st.append(‘ '); st.append(“to”); st.append(‘ ’); st.append(“Java"); st.append(2); //output: Welcome to Java2 Please make some note on the code. • StringBuffer provided overloaded methods to append boolean, char, char[], double, float, int, long, String.

16. The StringTokenizer • Count the number of words in a given String Example: Input: I am studying at NPIC Output: Word Count: 5 words

17. Test Count word • package teststring; • import java.util.StringTokenizer; public class Countword { • public static void main(String[]args){ • String s = javax.swing.JOptionPane.showInputDialog(""); • StringTokenizer token = new StringTokenizer(s); • System.out.println(""+token.countTokens()); • } • }

18. Lab Exerise 2 • On page 276, Section 8.4.3 The StringBuffer Class Home work write code page 276 8.3