Java String Methods

In the previous section we learned about loops in java and what are the 3 types of loops, Now in this section we are going to learn most usable topic in entire java programming language "Java Strings".  String is a widely used topic in Java programming, Strings are a sequence of characters. In Java, strings are treated as objects. The Java platform provides the String class to create and manipulate strings

How do we create a string in Java?

We have different ways to create a string in java, the most common way to create a String is 

String helloString = "Hello world";

We can also create a String with "new" keyword

Create a String with "new" Keyword

 String helloString = new String("Hello world"); 

So what is the difference between create String with new keyword and double quotes ("")

new String("Hello world"); which explicitly creates a new  distinct instance of a String object; 

where as String helloString = "Hello world";  it  may reuse an instance from the string constant pool if one is available.

Note: The String class is immutable, so that once it is created a String object cannot be changed. If there is a necessity to make a lot of modifications to Strings of characters, then you should use String Buffer & String Builder Classes

We will learn about String buffer and String builder in coming sections.

This unit will cover even more methods for working with strings.

• length()

• trim()

• concat()

• toLowerCase()

• toUpperCase()

• startsWith()

• endsWith()

• replace()

Java String Methods

String length() method

Methods used to obtain information about an object are known as accessor methods. One accessor method that you can use with strings is the length() method, which returns the number of characters contained in the string object

Syntax

Example

public class StringDemo {

   public static void main(String args[]) {
      String javaString = "welcome to Java String";
      int len = javaString.length();
      System.out.println( "String Length is : " + len );
   }
}

Output

String Length is : 22

Concatenating Strings

The String class contains a method called concat to add different strings, int and other primitive types values...

Syntax:

string1.concat(string2);

The above  returns a new string that is string1 with string2 added to it at the end. We can also use the concat() method with string literals, as in −

"Java String ".concat("Methods");

Strings are more commonly concatenated with the + operator, as in −

"Hello," + " world" + "!"

This will returns 

"Hello, world!"

Java String trim() method

The trim() method removes all the leading(starting) and trailing(ending) spaces of the given string and returns a new string.

Syntax

str.trim();

Example

Output

  9876543210

9876543210

In the above code, we can see that the trimmed variable contains a new string returned by trim() after removing all the leading and trailing spaces.

toLowerCase()

The toLowerCase() method converts each character of the given string to lowercase and returns a new string.

Syntax

str.toLowerCase();

Example

Output

HEllO, How ARE yOu?

hello, how are you?

In the above code, we can see that the lowercaseStr variable contains a new string returned by toLowerCase() with all the characters of the given string converted to lowercase. 

toUpperCase()

The toUpperCase() method converts each character of the given string to uppercase and returns a new string.

Syntax

str.toUpperCase();

Example

Output

helLO, How aRe yoU?

HELLO, HOW ARE YOU?

In the above code, we can see that the uppercaseStr variable contains a new string returned by toUpperCase() with all the characters of the given string converted to uppercase.

startsWith()

The startswith() method returns true if the given string starts with the specified value. Otherwise, false is returned.

Syntax

str.startsWith(value);

The value provided to startswith() should be a string.

Example

Output

true

In the above code, the url starts with https://. Hence true is returned and printed to the console.

endsWith()

The endsWith() method returns true if the given string ends with the specified value. Otherwise, false is returned.

Syntax

str.endsWith(value);

The value provided to endsWith() should be a string.

Example

Output

true

In the above code, the gmailId ends with @gmail.com. Hence true is returned and printed to the console.

Java Replace Methods

replace()

The replace() method in Java works similar to that in Python. It replaces all the occurrences of the old character/substring with the latest character/substring and returns a new string.

Syntax

The old and latest can be either characters (char) or strings.

Note: Both old and latest should be of the same data type.

Example 

Output

Jeve

In the above code, we can see that replace() returns a new string replacing all the occurrences of a with e.

Example 2:

Output

the cat and the dog

Java replaceFirst()

The replaceFirst() method returns a new string after replacing the first occurrence of the old substring with the latest substring.

Syntax

Example

Output

the cat and teh dog

In the above code, we can see that the replaceFirst() method returns a new string replacing only the first occurrence of teh to the

What if a character is to be replaced using replaceFirst()? The replaceFirst() method accepts strings but not characters (i.e, char data type).

Wrong  Code

Output

The error occurs because we cannot pass a char data type to replaceFirst(). To meet the requirement, we can provide double quotes (") around characters to pass the characters as strings.

Executed Code

Output

Java

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