Reverse a string without using string functions

Question

How to write a java program to reverse a string without using string functions?

 String a="Siva";

 for(int i=0;i<=a.length()-1;i++)
 {
     System.out.print(a.charAt(i));
 }
     System.out.println("");

 for(int i = a.length() - 1; i >= 0; --i)
 {
     System.out.print(a.charAt(i)); 
 }

here charAt() and a.length() are string functions

Do you want to reverse the string itself or just print it reversed? — ItayB, Dec 05 '13 at 06:52
Without using *any* methods, you simply can't get at the data. Presumably this is homework, so I suggest you ask your tutor which methods you *are* allowed to use. — Jon Skeet, Dec 05 '13 at 06:55
Without using any String methods we cant reverse a a string? — Jeevan Roy dsouza, Dec 05 '13 at 06:59
Refer http://learnjava-soa.blogspot.in/2016/02/write-java-program-without-using.html — madhu, Feb 15 '16 at 07:17

score 7 · Answer 1 · edited Dec 05 '13 at 07:21

7

This will help

public class StringReverse {

   public static void main(String[] args){
    String str = "Reverse";
    StringBuilder sb = new StringBuilder(str);
    str = sb.reverse().toString();
    System.out.println("ReverseString : "+str);
  }

}

There is no usage of String methods

edited Dec 05 '13 at 07:21

Deepak

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answered Dec 05 '13 at 06:58

Keerthivasan

12,760
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1

str.toCharArray() is a string function – Jeevan Roy dsouza Dec 05 '13 at 07:07
Pff, i went till. String str = "test"; Matcher m = Pattern.compile("$").matcher(str); m.find(); int length = m.end(); – Abhishek Anand Dec 05 '13 at 07:32

score 3 · Answer 2 · answered Dec 05 '13 at 07:00

3

String s = "abcdef";
char c[] = s.toCharArray();

for( int i = c.length -1; i>=0; i--)
    System.out.print(c[i]);

answered Dec 05 '13 at 07:00

laksys

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length() is string function – Jeevan Roy dsouza Dec 05 '13 at 07:06
It is length not length() – laksys Dec 05 '13 at 07:09
`toCharArray()` string functions. – Michael Kazarian Dec 05 '13 at 07:10
s.toCharArray() array is a string function – Jeevan Roy dsouza Dec 05 '13 at 07:11
1

Considering Java I think we cannot accomplish reverse without using functions since it does not support pointers directly. – laksys Dec 05 '13 at 07:14

Deepak · Answer 3 · 2013-12-05T07:11:40.433

Use StringBuilder class or StringBuffer class they have already a method reverse() for reversing the string

StringBuilder str = new StringBuilder("india");
System.out.println("string = " + str);

// reverse characters of the StringBuilder and prints it
System.out.println("reverse = " + str.reverse());

// reverse is equivalent to the actual
str = new StringBuilder("malayalam");
System.out.println("string = " + str);

// reverse characters of the StringBuilder and prints it
System.out.println("reverse = " + str.reverse());

http://docs.oracle.com/javase/7/docs/api/java/lang/StringBuilder.html

Michael Kazarian · Answer 4 · 2013-12-05T08:08:22.917

Below is ugly hack. It concept but it not invoke any String methods.

import java.io.*;
import java.util.*;
public class Hello {
    public static String reverceWithoutStringMethods(String word){
        String result = "";
        //------ Write string to file -----------
        BufferedWriter writer = null;
        try {
            writer = new BufferedWriter( new FileWriter("tempfile"));
            writer.write(word);
        }
        catch ( IOException e) {}
        finally {
            try{
                if ( writer != null) writer.close( );
            }
            catch ( IOException e){}
        }
        //------ read string from file -------------
        RandomAccessFile f=null;
        try {
             f = new RandomAccessFile("tempfile", "r"); // Open file
            int length = (int) f.length(); // Get length
            // Read file
            byte[] data = new byte[length];
            f.readFully(data);
            // Reverse data
            for (int i=data.length; i>=0; i--){
                result += (char)data[i-1];
            }
        } catch(Exception e){}
        finally {
            try{
                f.close();
            }
            catch (Exception e){}
        }
        return result;
    }
    public static void main(String[] args) { 
        System.out.println(reverceWithoutStringMethods("Test"));
        System.out.println(reverceWithoutStringMethods(""));
    } 
}

Output:

tseT

@JeevanRoydsouza see update.It not invoke any String method. — Michael Kazarian, Dec 05 '13 at 08:09

Reverse a string without using string functions

4 Answers4