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How to read user input from Console in Java using Scanner Example

Posted: 08 Dec 2012 05:39 AM PST

Apart from reading file, Scanner can also read user input from Console in Java. Just like in case of reading file, we have provided File as source for scanning, We need to provide System.in as source to scan for user input in Console. Once you created and initialized java.util.Scanner, you can use its various read method to read input from user. If you want to read String, you can use nextLine(), if you want to read integer numbers, you can use nextInt(). Subsequently you can use nextFloat() to read float input, nextDouble() to read double input etc. Scanner class also allows you to define your own pattern and scan for that.

How to reverse String in Java with or without StringBuffer Example

Posted: 08 Dec 2012 03:04 AM PST

Reverse String in Java

There are many ways to reverse String in Java. You can use rich Java API to quickly reverse contents of any String object. Java library provides StringBuffer and StringBuilder class with reverse() method which can be used to reverse String in Java. Since converting between String and StringBuffer or StringBuilder is very easy it's the most easy way available to reverse String in Java. At the same time Writing Java program to reverse String in Java without StringBuffer is one of the popular Java String interview question, which requires you to reverse String by applying logic and by not using API methods. Since reverse is a recursive job, you can use recursion as well as loop to reverse String in Java. In this Java tutorial I have shown How to reverse String using StringBuffer, StringBuilder and using pure loop with logic. You can also check How to reverse String with recursion in Java, if you want to see recursive code. let's see complete Java program for this beautiful Java programming exercise.

Java program to reverse String in Java

Here is my complete code program to reverse any String in Java. In main method we have first used StringBuffer and StringBuilder to reverse contents of String and then we wrote our own logic to reverse String. This uses toCharArray() method of String class which return character array of String. By looping through character array and appending it into empty String we can get reversed String in Java, as shown in following example.

/**
*
* Java program to reverse String in Java. There are multiple ways to reverse
* String in Java, you can either take help of standard Java API StringBuffer
* to reverse String in Java. StringBuffer has a reverse() method which return StringBuffer
* with reversed contents. On the other hand you can also reverse it by applying your
* own logic, if asked to reverse String without using StringBuffer in Java. By the way
* you can also use StringBuilder to reverse String in Java. StringBuilder is non thread-safe
* version of StringBuffer and provides similar API. You can use StringBuilder's reverse()
* method to reverse content and then convert it back to String
*
* @author http://java67.blogspot.com
*/
public class StringReverseExample {

public static void main(String args[]) {

//quick wasy to reverse String in Java - Use StringBuffer
String word = "HelloWorld";
String reverse = new StringBuffer(word).reverse().toString();
System.out.printf(" original String : %s , reversed String %s %n", word, reverse);

//another quick to reverse String in Java - use StringBuilder
word = "WakeUp";
reverse = new StringBuilder(word).reverse().toString();
System.out.printf(" original String : %s , reversed String %s %n", word, reverse);

//one way to reverse String without using StringBuffer or StringBuilder is writing

//own utility method
word = "Band";
reverse = reverse(word);
System.out.printf(" original String : %s , reversed String %s %n", word, reverse);
}

public static String reverse(String source){
if(source == null || source.isEmpty()){
return source;
}
String reverse = "";
for(int i = source.length() -1; i>=0; i--){
reverse = reverse + source.charAt(i);
}

return reverse;
}

}

Output:
original String : HelloWorld , reversed String dlroWolleH
original String : WakeUp , reversed String pUekaW
original String : Band , reversed String dnaB

That's all on How to reverse String in Java with and without StringBuffer and StringBuilder. Though being a Java programmer I prefer to use library and suggest any one to use StringBuffer or StringBuilder to reverse String for any production use. Though its also a good programming exercise and you should practice it before going for any Java programming interview.

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