There are a number of methods that search string to determine if a string starts or ends with a particular character or set of characters, or determine if a certain character is at a specific location, etc. These are:

• The startsWith( ) method that will return true if the argument matches the relevant start character(s) of a given string.
• The endsWith( ) method that will return true if the argument matches the relevant end character(s) of a given string.
• The charAt( ) method that returns the character at a specified index position within a string.
• The indexOf( ) method that returns the index position of a specified character within a string.

startsWith() method & endsWith() Methods

These methods will return true if their argument matches the relevant start or end character(s) of a given string. They are useful when you need to check a string before you use it.

Using the the string schoolString = “Learning Glue” let’s check to see if it starts with Learning or Glue.

String schoolString = "Learning Glue";
System.out.println("Our string is: " + schoolString);

//Check if the string starts with "Learning"
System.out.println("Does it start with Learning: " + schoolString.startsWith("Learning"));

//Check if the string starts with "Glue"
System.out.println("Does it start with Glue: " + schoolString.startsWith("Glue"));

Since these methods will return a boolean we can expect a true or false to our questions. The output should be:

run:
Our string is: Learning Glue
Does it start with Learning: true
Does it start with Glue: false
BUILD SUCCESSFUL (total time: 0 seconds)

charAt() Method

Since a string is essentially a collection of individual characters, or an array of chars, we can pinpoint any individual character by specifying its index. We can do this using the charAt( ) method which allows us to specify an index position within a string to return that character. The general syntax is:

string.charAt(num);

Using our schoolString variable (“Learning Glue”), let’s see this method in action:

String schoolString = "Learning Glue";

//Returns the first character
char ch1 = schoolString.charAt(0);

//Returns the third character
char ch2 = schoolString.charAt(3);

//Returns the fifth character
char ch3 = schoolString.charAt(5);

//Returns the tenth character
char ch4 = schoolString.charAt(10);

System.out.println("Our string is: " + schoolString);
System.out.println("The character at index 0 is: " + ch1)
System.out.println("The character at index 3 is: " + ch2)
System.out.println("The character at index 5 is: " + ch3)
System.out.println("The character at index 10 is: " + ch4);

The output returns the character at each index location within the string:

run:
Our string is: Learning Glue
The character at 0 index is: L
The character at index 3 is: r
The character at index 5 is: i
The character at index 10 is: l
BUILD SUCCESSFUL (total time: 0 seconds)

indexOf( ) Method

The indexOf( ) method will return the index position of the first occurrence of a character or the starting index position of a string. The general syntax for a char is:

string.indexOf(‘char’);

or for a string:

string.indexOf(“string”);

The indexOf( ) method is case sensitive, so “glue” with a lower case g is very different from “Glue” with an uppercase G.  Using our schoolString variable (“Learning Glue”), let’s see this method in action:

String schoolString = "Learning Glue";

//Finds the index position of the first instance of the character 'e'         
int charLocation = schoolString.indexOf('G');

//Finds the index position of the first instance of the string 'Glue'
int stringLocation = schoolString.indexOf("Glue");

//Finds the index position of the first space
int spaceLocation = schoolString.indexOf(' ');

//Outputs the string and index locations of the above characters and string
System.out.println("Our string is: " + schoolString); 
System.out.println("The index of the first char G is: " + charLocation);
System.out.println("The index of the string Glue is: " + stringLocation);
System.out.println("The index of the first space is: " + spaceLocation);

The output returns the index location for the first occurrence of the character ‘G’, the string “Glue” and the first space in the string “Learning Glue”:

run:
Our string is: Learning Glue
The index of the first char G is: 9
The index of the first string Glue is: 9
The index of the first space is: 8
BUILD SUCCESSFUL (total time: 0 seconds)

The index position of any character or string of characters can be found using the indexOf( ) method.

Remember that the indexOf( ) method is case sensitive and index positions always start from 0.

If the indexOf( ) method cannot find a character or string, it will return -1.