» Details on Java String Class with Examples and Methods - String

1) Strings are immutable and final in Java
Strings are immutable in Java it means once created you cannot modify content of String. If you modify it by using toLowerCase(), toUpperCase() or any other method,  It always result in new String. Since String is final there is no way anyone can extend String or override any of String functionality.

 

2) Strings are maintained in String Pool

Advanced Java String tutorial and example programmers As I Said earlier String is special class in Java and all String literal e.g. "abc"  (anything which is inside double quotes are String literal in Java) are maintained in a separate String pool, special memory location inside Java memory, more precisely inside PermGen Space. Anytime you create a new String object using String literal, JVM first checks String pool and if an object with similar content available, than it returns that and doesn't create a new object. JVM doesn't perform String pool check if you create object using new operator.

3) Use Equals methods for comparing String in Java

String class overrides equals method and provides a content equality, which is based on characters, case and order. So if you want to compare two String object, to check whether they are same or not, always use equals() method instead of equality operator. Like in earlier example if  we use equals method to compare objects, they will be equal to each other because they all contains same contents. Here is example of comparing String using equals method.

 

4) Use SubString to get part of String in Java

Java String provides another useful method called substring(), which can be used to get parts of String. basically you specify start and end index and substring() method returns character from that range. Index starts from 0 and goes till String.length()-1. By the way String.length() returns you number of characters in String, including white spaces like tab, space. One point which is worth remembering here is that substring is also backed up by character array, which is used by original String. This can be dangerous if original string object is very large and substring is very small, because even a small fraction can hold reference of complete array and prevents it from being garbage collected even if there is no other reference for that particular String.

 

5) "+" is overloaded for String concatenation

Java doesn't support Operator overloading but String is special and + operator can be used to concatenate two Strings. It can even used to convert int, char, long or double to convert into String by simply concatenating with empty string "". internally + is implemented using StringBuffer prior to Java 5 and StringBuilder from Java 5 onwards. This also brings point of using StringBuffer or StringBuilder for manipulating String. Since both represent mutable object they can be used to reduce string garbage created because of temporary String.
     

6) Use trim() to remove white spaces from String

String in Java provides trim() method to remove white space from both end of String. If trim() removes white spaces it returns a new String otherwise it returns same String. Along with trim() String also provides replace() and replaceAll() method for replacing characters from String. replaceAll method even support regular expression.

7) Use split() for splitting String using Regular expression

String in Java is feature rich. it has methods like split(regex) which can take any String in form of regular expression and split the String based on that. particularly useful if you dealing with comma separated file (csv) and wanted to have individual part in a String array.