Introduction to String Functions in Java:
Number of methods provided in Java to perform operations in Strings is called String functions. The methods are compare(), concat(), equals(), split(), length(), replace(), compareTo() and so on. Strings in Java are constant and it is created either using a literal or using a keyword. String literal is used to make Java memory efficient and the keyword creates Java string in normal memory. The string represents an array of character values and the class is implemented by three interfaces such as Serializable, Comparable, and CharSequence interfaces. It represents the sequence of characters in a serialized or comparable manner.
Main Concept of string functions in Java
- Creating String: There are two ways in which a String object can be created in Java:
Using a string literal: String literal in Java can be created using double-quotes.
Example: String s= “Hello World!”;
Using the new keyword: Java String can be created by using a keyword “new”.
Example: String s=new String (“Hello World!”);
- String length: Methods which are used to get information about an object are called accessor methods in Java. One such accessor method related to strings is the length () method. This returns the number of characters in the string object.
public class Exercise {
public static void main(String args[]{
String s1="Hello";
String s2="World";
System.out.println("string length is: "+s1.length());
System.out.println("string length is: "+s2.length());
}}
- Concatenating string: This method returns a new string which is string1 with string2 combined at the end. Concat () method can be used with string literals to get this done. Strings are also commonly concatenated using + operator.
public class ExerciseNew {
public static void main(String args[]){
String s1="Hello";
s1=s1.concat("What is your good name?");
System.out.println(s1);
}}
- Creating a format string: We have printf () and format () methods that prints output with formatted numbers. There is an equivalent class method in String called format (). It returns a String object. Static format () method available in String object allows creating a formatted string which can be reused, contrary to the one-time print statement.
Methods of string functions in Java
Following are the different methods:
| Method | Description |
| char charAt(int index) | It returns the char value of the particular index as mentioned. |
| int length() | It returns the length of the string |
| static String format(String format, Object… args) | It returns a string which is duly formatted. |
| static String format(Locale l, String format, Object… args) | It returns formatted string along with given locale. |
| String substring(int beginIndex) | It returns substring which starts from begin index. |
| String substring(int beginIndex, int endIndex) | It returns substring for given start index position and ends index. |
| boolean contains(CharSequence s) | It returns true or false after doing a match between the sequence of char value. |
| static String join(CharSequence delimiter, CharSequence… elements) | It returns a string which is joined |
| static String join(CharSequence delimiter, Iterable<? extends CharSequence> elements) | It returns a joined string same as above. |
| boolean equals(Object another) | It checks the equality of string. It does so with the given object. |
| boolean isEmpty() | It checks if a given string is empty or not. |
| String concat(String str) | It concatenates the specified string as above example. |
| String replace(char old, char new) | It replaces all occurrences of the specified old char value. With new value. |
| String replace(CharSequence old, CharSequence new) | It replaces all occurrences of the given specified CharSequence with the new one. |
| static String equalsIgnoreCase(String another) | It compares with another string but It is not case sensitive. |
| String[] split(String regex) | It returns a split string based on matching the regex. |
| String[] split(String regex, int limit) | It returns a split string which matches regex and limit. |
| String intern() | It returns a string which is interned. |
| int indexOf(int ch) | It returns the selected char value index. |
| int indexOf(int ch, int fromIndex) | It returns the specified char value index which starts with a given index. |
| int indexOf(String substring) | It returns the selected substring index. |
| int indexOf(String substring, int fromIndex) | It returns the selected substring index which starts with a given index. |
| String toLowerCase() | It returns a string with all chars in lowercase. |
| String toLowerCase(Locale l) | It returns a string in lowercase with specified locale. |
| String toUpperCase() | It returns a string with all chars in uppercase. |
| String toUpperCase(Locale l) | Same as above but with specified locale. |
| String trim() | It removes the starting and ending whitespaces of this string. |
| static String valueOf(int value) | It converts another data type into a string. It is called an overloaded method. |
Examples of functions in Java
In this section, we have discussed some examples of string functions in Java.
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Example #1: Check if a string is empty
public class IsEmptyExercise{
public static void main(String args[]){
String s1="";
String s2="Hello";
System.out.println(s1.isEmpty()); // true
System.out.println(s2.isEmpty()); // false
}}
Example #2: Trim whitespaces in a string
public class StringTrimExercise{
public static void main(String args[]){
String s1=" HelloWorld ";
System.out.println(s1+"How are you doing today"); // without trim()
System.out.println(s1.trim()+"How are you doing today"); // with trim()
}}
Example #3: Convert a string to lowercase
public class StringLowerExercise{
public static void main(String args[]){
String s1="HELLO HOW Are You TODAY?”;
String s1lower=s1.toLowerCase();
System.out.println(s1lower);}
}
Example #4: Replace a part of a string
public class ReplaceExercise{
public static void main(String args[]){
String s1="hello how are you today";
String replaceString=s1.replace('h','t');
System.out.println(replaceString); }}
Example #5: Check if two strings are equal
public class EqualsExercise{
public static void main(String args[]){
String s1="Hi";
String s2="Hey";
String s3="Hello";
System.out.println(s1.equalsIgnoreCase(s2)); // returns true
System.out.println(s1.equalsIgnoreCase(s3)); // returns false
}
}
Conclusion
Apart from the above-mentioned characteristics, functions, and methods, there are other facts too with the String class. String class is a final class and that is the reason String class objects are immutable in nature. A special memory area is reserved by JVM for string classes, this area is called String constant pool.
In the String library, available with java. Lang, overriding the String references are possible but the content or literals cannot be copied. Any number which is closed in double-quotes also treated as the string.
Students should test these codes in an IDE and make the necessary modification here and there to further enhance their understanding. String manipulation is very important to know in any programming language and it is used on a daily basis by developers.
Recommended Articles
This has been a guide to String functions in Java. Here we have discussed the different methods of string functions in java with examples. You may also look at the following article to learn more –
