String class functions

The following are the most commonly used functions of the String class:

The charAt() function

The following line of code is an example of the charAt() function in a Java program:

public char charAt(int index)

The charAt() function returns the char value at the specified index. An index ranges from 0 to length() - 1. The first char value of the sequence is at index 0, the next at index 1, and so on, as for array indexing. The following is another example:

String str = "welcome";
System.out.println(str.charAt(2));

The output is displayed here:

l

The equalsIgnoreCase() function

The following line of code is an example of the equalsIgnoreCase() function in a Java program. It compares one String to another String, ignoring case considerations. Two strings are considered equal ignoring case if they are of the same length, and corresponding characters in the two strings are equal ignoring case.

String str = "java";
System.out.println(str.equalsIgnoreCase("JAVA"));

The output will be as follows:

true

The length() function

The following line of code is an example of the length*() function in a Java program:

public int length()

The length() function returns the length of this string. The length is equal to the number of Unicode code units in the string:

String str = "Welcome";
System.out.println(str.length());

The output will be as follows:

7

The replace() function

The following line of code is an example of the replace() function in a Java program:

public String replaceAll(String regex, String replacement)

The replace() function returns a new string resulting from replacing all occurrences of oldChar in this string with newChar:

String str = "Java programming";
System.out.println(str.replace('p','P'));

The output will be as follows:

Java Programming

The substring() function

The following line of code is an example of the substring() function in a Java program:

public String substring(int beginIndex)

The substring() function returns a new string that is a substring of this string. The substring begins with the character at the specified index and extends to the end of this string:

String str = "Java Programming";
System.out.println(str.substring(5));

The output will be as follows:

Programming

The following line of code is another example of the substring() function in a Java program:

public String substring(int beginIndex, int endIndex)

This returns a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at the index endIndex - 1. Thus, the length of the substring is endIndex-beginIndex:

String str = "Java Programming";
System.out.println(str.substring(5,11));

The output will be as follows:

Program

The toLowerCase() function

The following line of code is an example of the toLowerCase() function in a Java program:

public String toLowerCase()

The toLowerCase() function converts all of the characters in this String to lowercase using the rules of the default locale:

String str = "JAVA";
System.out.println(str.toLowerCase());

The output will be as follows:

java

The toUpperCase() function

The following line of code is an example of the toUpperCase() function in a Java program:

public String toUpperCase()

The toUpperCase() function converts all of the characters in this String to uppercase using the rules of the default locale:

String str = "java";
System.out.println(str.toUpperCase());

The output will be as follows:

JAVA

The trim() function

The following line of code is an example of the trim() function in a Java program:

public String trim()

The trim() function returns a copy of the string, with leading and trailing whitespace omitted. This method can be used to trim whitespace from the beginning and end of a string:

String str = "   Java  ";
System.out.println(str.trim());

The output will be as follows:

Java

Note

Following is a link on more information on String class methods:

https://docs.oracle.com/javase/6/docs/api/java/lang/String.html