Java String Methods

Strings in Java are objects that represent sequences of characters. The String class in Java is used to create and manipulate string data. Here are some fundamental aspects of strings in Java, including how to use various String methods with examples and explanations.

Creating Strings

Strings can be created in Java in several ways:

Common String Methods

Java provides numerous methods within the String class to perform operations on strings.


Returns the length of a string (number of characters).

charAt(int index)

Returns the character at the specified index.

substring(int beginIndex, int endIndex)

Returns a substring of the string, starting from beginIndex to endIndex (exclusive).

contains(CharSequence s)

Returns true if the string contains the specified sequence of char values.

equals(Object anotherObject)

Compares this string to the specified object.

equalsIgnoreCase(String anotherString)

Compares this String to another String, ignoring case considerations.

startsWith(String prefix) and endsWith(String suffix)

Check if the string starts or ends with the given prefix or suffix.

replace(char oldChar, char newChar)

Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.

toUpperCase() and toLowerCase()

Converts all the characters in the string to upper case or lower case.


Removes whitespace from both ends of a string.

split(String regex)

Splits this string around matches of the given regular expression.

Method indexOf

The indexOf method in Java’s String class is another essential tool for string manipulation. It returns the index within this string of the first occurrence of the specified character or substring. If the character or substring is not found, then -1 is returned. There are several overloads of this method to handle different scenarios.

indexOf(int ch)

Finds the index of the first occurrence of a specified character.


In this example, indexOf searches for the character ‘J’ in the string and returns 7, which is the position where ‘J’ is found.

indexOf(int ch, int fromIndex)

Finds the index of the first occurrence of a specified character, starting the search at the specified index.


Here, indexOf searches for ‘a’ starting from index 8, finding it at position 9.

indexOf(String str)

Finds the index of the first occurrence of a specified substring.


This indexOf method looks for the substring “Java” and returns 7, indicating the starting position of the substring within the string.

indexOf(String str, int fromIndex)

Finds the index of the first occurrence of a specified substring, starting the search at the specified index.


In this case, indexOf starts looking for “Java” from index 5 and finds it at index 8, which is the start of the second occurrence of “Java” in the string.

The indexOf method is incredibly useful for determining the presence and position of characters or substrings within a string. It can be used for tasks such as parsing data, validating input, or simply checking for the existence of certain text within a larger string. Understanding how to use indexOf effectively can greatly enhance your ability to work with strings in Java.

valueOf Method

The valueOf method in Java’s String class is a static method that converts different data types into their corresponding string representation. It is an overloaded method, capable of handling various input types, including objects, primitives, and character arrays. This method is particularly useful when you need to concatenate different data types or when you need to convert a non-string type to a string for processing.

valueOf Method Overloads

Here are some examples of using valueOf with different data types:


In these examples, valueOf converts an integer and a double to their respective string representations.

Character Array

Here, valueOf is used to convert an array of characters into a string.


This example demonstrates converting a boolean value to a string.

Using valueOf with Objects

valueOf can also be used with objects. If the object is null, valueOf returns the string "null". Otherwise, it calls the toString method on the object.

In this case, valueOf is used to convert an Integer object into a string. If integerObject were null, "null" would be printed instead.

Practical Use Case

A common use case for valueOf is in concatenation operations where you need to ensure that values are strings to avoid unexpected behavior.

Without valueOf, adding age directly would also work due to Java’s automatic conversion during string concatenation. However, explicitly converting values to strings can make the code’s intention clearer and avoid confusion in more complex scenarios.

The valueOf method is a versatile and powerful tool for converting various data types to strings, facilitating operations that require string manipulation and representation of non-string values.

Understanding and utilizing these String methods allows you to effectively manipulate and process text data in Java, making it an essential skill for any Java developer. These methods cover a wide range of operations from basic string manipulation to more complex text processing tasks.

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