Replacing data using java

Question

I would like to replace data in a file with some new data and rename the file with a different name in java. I have the old file saved in the same class directory as the code to carry out the changes is saved. The command that I use in the command prompt is as below.

java ReplacingText oldfile newfile oldstring newstring

I get the error:

Exception in thread "main" java.lang.NoClassDefFoundError: ReplacingText (wrong name: replacingtext/ReplacingText)
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)

Could someone shed some light on it.

package replacingtext;

import java.io.*;
import java.util.*;

public class ReplacingText 
{
    public static void main(String[] args) throws Exception
    {

        if (args.length !=4)
        {
            System.out.println(
            "Usage: java ReplaceText sourceFile targetFile oldStr newStr");
            System.exit(0);
        }
        File sourceFile = new File(args[0]);
        if(!sourceFile.exists())
        {
            System.out.println("Source file " + args[0]+" does not exist");
            System.exit(0);
        }
        File targetFile = new File(args[1]);
        if (targetFile.exists())
        {
            System.out.println("Target File " + args[1] + "already exist");
            System.exit(0);
        }
        Scanner input = new Scanner(sourceFile);
        PrintWriter output2 = new PrintWriter(targetFile);

        while (input.hasNext())
        {
            String s1=input.nextLine();
            String s2=s1.replaceAll(args[2],args[3]);
            output2.println(s2);
        }
        input.close();
        output2.close();
    }
}

Answer 1

i found it on the net. first, i make a direcoty,name as "replacingtext" ,the package name. then, i move the complied class "ReplacingText.class" into it. last, i run "java replacingtext.ReplacingText "c:/s.txt" "c:/t.txt" haha yes" in "replacingtext" parent directory.

bingo...it works..

but.. i don't konw why.. perhaps the classLoader find the class by the relative path ,not just the class name...

Answer 2

first,i tested the method like this.

public static void main(String[] args) throws Exception {

        String sourceFile = "c://s.txt";
        String targetFile = "c://t.txt";
        String oldS = "haha";
        String newS = "yes";
        test(new String[]{sourceFile,targetFile,oldS,newS});

        //      test(args);
    }

    private static void test(String[] args) throws FileNotFoundException {
        // TODO Auto-generated method stub
        if (args.length != 4) {
            System.out
                    .println("Usage: java ReplaceText sourceFile targetFile oldStr newStr");
            System.exit(0);
        }
        File sourceFile = new File(args[0]);
        if (!sourceFile.exists()) {
            System.out.println("Source file " + args[0] + " does not exist");
            System.exit(0);
        }
        File targetFile = new File(args[1]);
        if (targetFile.exists()) {
            System.out.println("Target File " + args[1] + " already exist");
            System.exit(0);
        }
        Scanner input = new Scanner(sourceFile);
        PrintWriter output2 = new PrintWriter(targetFile);

        while (input.hasNext()) {
            String s1 = input.nextLine();
            String s2 = s1.replaceAll(args[2], args[3]);
            output2.println(s2);
        }
        input.close();
        output2.close();
    }

it works.

then, i tested based on the method above like this.

public static void main(String[] args) throws Exception {
        test(args);
}

java ReplacingText c://s.txt c://t.txt haha yes

it worked ,too..

ps:cause i didn't config the JAVA_HOME,so I run it in my jdk/bin directory.