如何优化以下代码以更好地使用内存？

Question

/* package codechef; // don't place package name! */
import java.util.StringTokenizer;
import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */

class Codechef
{

     String func (String s1)
    {
        StringTokenizer st =new StringTokenizer(s1);
        String fina= new String();
            while(st.hasMoreTokens())
            {
                String s= st.nextToken();
                char []ch= s.toCharArray(); 
                int length= ch.length;
                int r=0;
                int i =1;
                while(i<=length/2)
                    {  

                        char temp;
                        temp=ch[i];
                        ch[i]=ch[length-1-r];
                        ch[length-1-r]=temp;
                        r++;
                        i++;
                     }


                String revword=new String(ch);
                fina+=""+revword +" ";

            }

            return(fina);

    }

    public static void main (String[] args) throws java.lang.Exception
    {
        String s1="Tarun is a intern";  
        Codechef c=new Codechef();
        String s2=c.func(s1);
        System.out.println(""+s2);
    }
}

The above code was run on codechef ide i am using 2638 KB of memory . Is there any other method I can use to decrease the memory usage? Or any other optimized method? I tried using StringBuilder to append as it is mutable still it was giving me same memory usage on code chef.

Answer 1

This question would probably be better on codereview.stackexchange.com but nevertheless, I'll make some comments here.

Out of the 2638 KB of memory used, I expect the vast majority of that is used by the Java Runtime Environment, rather than directly by your application. Still you might make a few KB of savings. Here's a line-by-line commentary.

/* package codechef; // don't place package name! */

No need to keep the above line in your code.

import java.util.StringTokenizer;
import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */

class Codechef
{

     String func (String s1)
    {
        StringTokenizer st =new StringTokenizer(s1);

The documentation of StringTokenizer says this is a legacy class kept for backward compatibility and that newer code should use String.split() instead. This would improve readability, though I doubt it would improve performance or memory usage.

        String fina= new String();

Why are you using new String() ? Just use "" . By using new String() you are creating a new object, thus wasting a few bytes of memory, when "" refers to an existing object, and is more readable.

            while(st.hasMoreTokens())
            {
                String s= st.nextToken();
                char []ch= s.toCharArray(); 
                int length= ch.length;
                int r=0;

It may be slightly more readable to start r at 1 and use length-r instead of length-1-r .

                int i =1;

You need to start i at 0, as this is the index of the first character.

                while(i<=length/2)

It may be more readable to use a for loop.

                    {  

                        char temp;
                        temp=ch[i];

Why not declare and initialize on the same line? char temp = ch[i];

                        ch[i]=ch[length-1-r];
                        ch[length-1-r]=temp;
                        r++;
                        i++;
                     }


                String revword=new String(ch);
                fina+=""+revword +" ";

There is no need for the ""+ preceding revword. You are creating a new String by doing this (thus wasting memory). But revword is already a string, so no need to append it to a null string.

Appending to a String fina inside a loop costs CPU time (and some memory). You should use a StringBuilder instead.

Also, if you used StringBuilder you would have been able to copy ch to it directly, without having to create a new String that is a copy of ch .

            }

            return(fina);

Minor nit-pick: no need for parentheses here, as it makes the return keyword look like a method call, which it is not.

    }

By the way, your method adds a " " (space) at the end of the returned string, which is probably not what you want.

    public static void main (String[] args) throws java.lang.Exception
    {
        String s1="Tarun is a intern";  
        Codechef c=new Codechef();
        String s2=c.func(s1);
        System.out.println(""+s2);
    }
}