Basic string manipulation in Java with Real Examples : Part 1

Hi guys, how you doing today? I just noticed I haven't written anything about Java in quite some time now. Well let's bring Java back into the spotlight with this light subject on basic string manipulation.

Lets try to cover some simple examples covering different scenarios :

Illustration 1 : Extract a substring from a string

In this example we simply extract a part of the string.

public class String_manip {

public static void main(String[] args) {

 String str = "Hello guys. Welcome to IroncladZone";

 

 String sub_str = str.substring(23, 35);

 

 System.out.println (sub_str);

}

}

Output : IroncladZone

Illustration 2 : Replace a substring from a string

In this example we replace the word "guys" with "goodfellas" within the string.

public class String_manip {

public static void main(String[] args) {

String str = "Hello guys. Welcome to IroncladZone";

String replaced_str = str.replace("guys", "goodfellas");

System.out.println(replaced_str);

}

}

Output : Hello goodfellas. Welcome to IroncladZone

Note that strings are immutable. Their value cannot be changed once its created. However we can create a new string with the replaced word/part.

Illustration 3 : Join / Combine two strings i.e Concatenation

In this we simply join 3 strings together using +

public class String_manip {

public static void main(String[] args) {

String str1 = "Welcome";

String str2 = "to";

String str3 = "IroncladZone";

System.out.println(str1 + str2 + str3);

System.out.println(str1 + " " + str2 + " " + str3);

}

}

Output : 

WelcometoIroncladZone

Welcome to IroncladZone

Illustration 4 : Print the length of the string

public class String_manip {

public static void main(String[] args) {

String str = "Welcome to IroncladZone";

System.out.println(str.length());

}

}

Output :

23

Note the length() function used to show the length of the string.

Illustration 5 : Split a string on a whitespace

public class String_manip {

public static void main(String[] args) {

String str = "Welcome to IroncladZone";

String[] new_str = str.split("\\s+");

System.out.println(new_str[0]);

}

}

Output :

Welcome

Notice the \\s+ regex for the whitespace.

That's it for today fellas. I'll try to include some more advanced scenarios in a 2nd part of this post. There's more to come guys, stay tuned...

Check if a file exists using Java

I have long thought about including some content about Core Java concepts on my blog. So here is one of the first ones in the series, which covers some basic Java fundamentals. I assume you have some knowledge about using the Eclipse IDE for project creation. I also assume that you have some basic idea about the Java language (theoretical concepts like OOPS, Inheritance, Data abstraction etc). Don't worry if you don't know much because I plan to cover a few posts on those basics later.

At this point, this post here is all about writing a simple script in Java for checking if a specific file exists at a certain location. You may use the following example for quick reference.

Briefly speaking, we would be importing the java.io.File class and use one of it's methods - isFile.

Please note that the best preferred function to check if a files exists is exists(). In this example, we see how isFile() can also be used to check the same.

Here we go - Create a new class file in Eclipse named as "CheckFileExists_Example". If you maybe aware, the class name and filename has to be the same in Java.

package my.ironcladzone.com;

import java.io.IOException;
import java.io.File;

public class CheckFileExists_Example {

    public static void main(String[] args) {
            
            File f = new File("/usr/tmp/DocuTest.txt");
           
            if (f.isFile()) {
               
                System.out.println("File exists \n");
               
            } else {
       
                System.out.println("File does not exist \n");
            }
     }

}

Here, the method isFile is used to check if "DocuTest.txt" is a file or not. It returns a boolean value - true or false, depending on whethere it actually is a file or not. It will return false if the absolute path mentioned by us, turns out to be a directory.

Play around with code and check for yourself. Edit the path as just :

File f = new File("/usr/tmp/");

Now, the isFile function returns false since the path mentions the '/usr/tmp' location, which is a directory and not a file. So it will directly jump to the else block and print our "File does not exist" statement.

Try one more scenario - specify an imaginary filename in the path. Let's say for example xyz123.txt.

File f = new File("/usr/tmp/xyz123.txt");

It will return false if a filename xyz123.txt does not exist at a specific location.

The point here is how isFile() function can also be used, instead of traditional exists() function for checking if a specific filename exists. It serves a same-to-similar purpose.

I'd cover some more basic topics on I/O in Java i.e reading from files, writing to files in some future posts. So, stay tuned folks. In the meantime, do post your comments for any suggestions & tips. Ciao.