String Processing

String Class

Definition:

– Represents combinations of character literals

– Using Java, strings can be represented using:

        ● Array of characters

        ● The String class

                 – Note: A String object is different from an array of characters!

        ● String constructors

                 – 11 constructors

The StringBuffer Class

● Problem with String objects:

       – Once created, can no longer be modified (It is a final class)

● A StringBuffer object

       – Similar to a String object

       – But, mutable or can be modified

 ● Unlike String in this aspect

 ● Length and content may changed through some method calls

String Searching

There are several overloaded versions of the method indexOf() available in the String class for searching a string forward, the lastIndexOf() method for searching a string backward, and the regionMatches() method for comparing a “region” of text within a string.

The IndexOf() Method

SearchString.java

package com.appfworks.string;

/**
 * Created by suresh on 29/10/15.
 */
// Demonstrates searching a character in a string
public class SearchString {
    public static void main(String[] s) {
        String str = "OCPJP";
        // The indexOf() method searches the specified character— here it is, the character J— and
        // returns the first occurrence of the character (note that the index starts from 0, not 1!).
        System.out.println("Character J occurs at index: " + str.indexOf('J'));
        String str2 = "I am preparing for OCPJP";
        // The indexOf() method is overloaded, and one definition of the method takes a string as a
        // search argument.
        System.out.println("Substring \"for\" occurs at index: " + str2.indexOf("for"));
        String str3 = "I am a student. I am preparing for OCPJP";
        int fromIndex = 0;
        while(str3.indexOf("am", fromIndex) > -1) {
            fromIndex = str3.indexOf("am", fromIndex);
            System.out.println("Substring \"am\" occurs at index: " + fromIndex);
            fromIndex++;
        }
    }
}

The regionMatches() Method

MatchRegionInString.java

package com.appfworks.string;

/**
 * Created by suresh on 29/10/15.
 */
// This example demonstrates how to search a "region" of text within a string
public class MatchRegionInString {
    public static void main(String[] s) {
        String chat = "Tarzan: Hi Jane, wanna ride an Elephant? \n Jane: No thanks! I'm preparing for OCPJP now!";
        String matchString = " Jane: No thanks!";
        // first get the index of the position from which the search region starts
        int startIndex = chat.indexOf('\n');
        System.out.println("Jane's response starts at the index: " + startIndex);
        // if '\n' found, then try matching for the string " Jane: No thanks!" from there
        if(startIndex > -1) {
            // remember that the index starts from 0 and not 1, so add 1 to startIndex
            boolean doesMatch = chat.regionMatches(startIndex + 1, matchString, 0,
                    matchString.length());
            if(doesMatch)
                System.out.println("Jane's response matches with the string" +
                        matchString);
        }
    }
}

String Conversions

StringConvertions.java

package com.appfworks.string;

/**
 * Created by suresh on 29/10/15.
 */
public class StringConvertion {
    public static void main(String[] args){
        String str1 = String.valueOf(10); // right way to convert from an integer to String

    //    String str2 = 10; // compiler error—cannot convert from int to String
    //    String str3 = (String) 10; // compiler error—cannot convert from int to String

    //    int i = "10"; // compiler error—cannot convert from String to int
    //    int ii = (int) "10"; // compiler error—cannot convert from String to int

        int i1 = Integer.parseInt("10"); // right way to convert from a String to an int

        float f = Float.parseFloat("no such value");
    }
}

The Split() Method

ParseString.java

package com.appfworks.string;

/**
 * Created by suresh on 29/10/15.
 */
// this example demonstrates the usage of split() method
public class ParseString {
    public static void main(String[] s) {
        String quote = "Never lend books-nobody ever returns them!";
        String [] words = quote.split(" "); // split strings based on the delimiter " "(space)
        for (String word : words) {
            System.out.println(word);
        }

        String str = "c:\\work\\programs\\parser";
        String [] dirList = str.split("\\\\");
        for (int i=0; i<dirList.length; i++) {
            System.out.println(dirList[i]);
        }
    }
}

The Wrapper Classes

● Some Facts:

      – Primitive data types are not objects

               ● Cannot access methods of the Object class

      – Only actual objects can access methods of the Object class

      – Why wrapper classes?

               ● Need an object representation for the primitive type variables to use Java built-in methods

● Definition:

      – Object representations of simple non-object variables