How to replace a substring in Java?

You can replace a substring using replace() method in Java. The String class provides the overloaded version of the replace() method, but you need to use the replace(CharSequence target, CharSequence replacement). This version of the replace() method replaces each substring of this string (on which you call the replace() method) that matches the literal target sequence with the specified literal replacement sequence. For example, if you call "Effective Java".replace("Effective", "Head First") then it will replace "Effective" with "Head First" in the String "Effective Java". Since String is Immutable in Java, this call will produce a new String "Head First Java".

Read more »

How to check if String contains another SubString in Java? contains() and indexOf() example

You can use contains(), indexOf() and lastIndexOf() method to check if one String contains another String in Java or not. If a String contains another String then it's known as a substring. The indexOf() method accept a String and return starting position of the string if it exists, otherwise it will return -1. For example "fastfood".indexOf("food") will return 4 but "fastfood".indexOf("Pizza") will return -1. This is the easiest way to test if one String contains another substring or not. The second method is lastIndexOf() which is similar to indexOf() but start the search from the tail, but it will also return -1 if substring not found in the String or the last position of the substring, which could be anything between 0 and length -1.

Read more »

How to check if a String is numeric in Java? Use isNumeric() or isNumber()

In day-to-day programming, you often need to check if a given String  is numeric or not. It's also a good interview question but that's a separate topic of discussion. Even though you can use a Regular expression to check if given String is empty or not, as shown here, they are not full proof to handle all kinds of scenarios, which common third party library like Apache commons lang will handle e.g. hexadecimal and octal String. Hence, In Java application, the simplest way to determine if a String is a number or not is by using Apache Commons lang's isNumber() method, which checks whether the String a valid number in Java or not. Valid numbers include hexadecimal marked with the 0x or 0X qualifier, octal numbers, scientific notation and numbers marked with a type qualifier (e.g. 123L). Non-hexadecimal strings beginning with a leading zero are treated as octal values. Thus the string 09 will return false since 9 is not a valid octal value. However, numbers beginning with 0. are treated as decimal.null and empty/blank String will return false.

Read more »

How to split String in Java by WhiteSpace or tabs? Example Tutorial

You can split a String by whitespaces or tabs in Java by using the split() method of java.lang.String class. This method accepts a regular expression and you can pass a regex matching with whitespace to split the String where words are separated by spaces. Though this is not as straightforward as it seems, especially if you are not coding in Java regularly. Input String may contain leading and trailing spaces, it may contain multiple white spaces between words and words may also be separated by tabs. Your solution needs to take care of all these conditions if you just wants words and no empty String. In this article, I am going to show you a couple of examples to demonstrate how you can split String in Java by space. By splitting I mean getting individual words as String array or ArrayList of String, whatever you need.

Read more »

Difference in String pool between Java 6 and 7

String pool in Java is a pool of String literals and interned Strings in JVM for efficient use of String object. Since String is immutable in Java, it makes sense to cache and shares them in JVM. The String pool has gone through an important change in Java 7 release when it was relocated from PermGen space to heap space. Till Java 1.6, interned String and literals are stored in the PermGen space of JVM memory, which was a fixed size area for storing class metadata. The biggest issue of having String pool in PermGen is the small and fixed size of PermGen space. In some JVM it ranges from 32M to 96M, which is quite small for a large program. Since String is extensively used in both small and large Java application, Java designers thought String pool is the best way optimize the use of String object in Java.

Read more »