String Methods Java

In Java programming language, a string is nothing but a sequence of characters. It is the most widely used object. Java String class has many methods that are used for various manipulations. It is immutable, meaning, its value cannot be changed. A string is equivalent to an array of characters.

Creating a string in Java

We can create a string using 2 different methods:

• Using string literal
• Using new keyword

Create a string using a string literal

This is the most direct way of creating a string in Java. We can create a string by enclosing the value in double-quotes. Here the variable “value” of type String holds the string named as “Java language”

String value = "Java language";

When we create a string literal, JVM first checks in the “string constant pool” if the string exists. If it does not exist, JVM creates a new string instance, else only a reference to the pooled instance will be returned. For example, in the below case, both string objects hold the same value. Hence only 1 object is created (i.e s1) and s2 will have the reference to s1. This means, irrespective of how many ever string variables we create with the same value, only 1 instance will be created in the string constant pool.

“String constant pool” is nothing but the special memory to hold the string objects.

String s1 = "Java language"; 
String s2 = "Java language";

Creating a string using the new keyword

When we want to have 2 different objects holding the same string value, then we create a string using the new keyword as described below. In this case, JVM creates 2 different string objects in a heap memory

String s1 = new String("Java");
String s2 = new String("Java");

String Methods Java

The java.lang.String class supports various methods which are used for different string manipulations as described below:

Example: Java program to create a string from array characters

In the below example, we convert an array of characters to a string in Java using the new keyword.

public class StringDemo1 {

  public static void main(String[] args) {
    char[] c = {'j','a','v','a'};
    String s = new String(c);
    System.out.println(s);
    
  }

}

Output:
java

Example: Using length(), charAt() and indexOf() methods

The below example shows you how to retrieve a character at a particular index, get the length of a string, and retrieve the index of a particular character.

public class StringDemo2 {

  public static void main(String[] args) {
    String s1 = new String("Java tutorial");
    System.out.println("The character at index 6 is : " + s1.charAt(6));
    System.out.println("The length of the input string is : " + s1.length());
    System.out.println("The index of letter 'v' is : " + s1.indexOf('v'));
  }

}

Output:
The character at index 6 is : u
The length of the input string is : 13
The index of letter 'v' is : 2

Example: Using compareTo(), contentEquals() and contains()

This example shows a comparison of 2 strings in Java

1. compareTo() returns a positive integer here since the input string succeeds the argument string.
2. compareToIgnoreCase() returns 0 since both strings are equal irrespective of the case.
3. contains() returns true since the input string contains the argument string
4. contentEquals() returns false since the input string does not contain the exact argument string.

public class StringDemo2 {

  public static void main(String[] args) {
    String s1 = new String("Java tutorial");
    System.out.println("Comparison of input string with argument is : " + s1.compareTo("C++"));
    System.out.println("Comparison of input string with argument ignoring case is : " + s1.compareToIgnoreCase("JAVA TUTORIAL"));
    System.out.println("Output of contains method: " + s1.contains("tutorial"));
    System.out.println("Output of contentEquals method: " + s1.contentEquals("Java"));
    }
}

Output:
Comparison of input string with argument is : 7
Comparison of input string with argument ignoring case is : 0
Output of contains method: true
Output of contentEquals method: false

Example: Using equals()

1st output is false since the case does not match even though the content is the same. 2nd output is true since content and case matches.

3rd output is false since both content are different.

public class StringDemo3 {

  public static void main(String[] args) {
    String s1 = "java tutorial";
    String s2 = "Java Tutorial";
    String s3 = "java tutorial";
    String s4 = "Tutorial cup";
    System.out.println(s1.equals(s2));
    System.out.println(s1.equals(s3));
    System.out.println(s1.equals(s4));
  }

}

Output:
false
true
false

Example: Concatenation of strings

We can concatenate 2 strings in Java using concat() method of the Java String class. “+” is also used to concatenate 2 or more strings which are normally used in print statements. While concatenating 2 strings, space is not included in between the strings. In the below example, string s3 contains the concatenated value of s1 and s2 which is used along with a new string in the print statement.

We can also concatenate 2 strings in Java using the join() method. This will join the words passed in the argument with a delimiter specified.

public class StringConcat {

  public static void main(String[] args) {
    String s1 = "Hello,";
    String s2 = "how are you";
    String s3 = s1.concat(s2);
    System.out.println(s3 + " today");
    System.out.println(s1.join(",", "welcome","to","tutorialcup"));
  }

}

Output:
Hello,how are you today
welcome,to,tutorialcup

Example: Java program to convert string between upper case and lower case

public class StringCase {

  public static void main(String[] args) {
    String s1 = "Welcome to tutorialcup";
    System.out.println("Convert to lower case: " + s1.toLowerCase());
    System.out.println("Convert to upper case: " + s1.toUpperCase());

  }

}

Output:
Convert to lower case: welcome to tutorialcup
Convert to upper case: WELCOME TO TUTORIALCUP

Example: Using substring in Java

We can retrieve part of the string in Java using the substring method. The index value starts at 0.

public class StringDemo3 {

  public static void main(String[] args) {
    String s1 = "java tutorial";
    System.out.println(s1.substring(3));
    System.out.println(s1.substring(1, 10));
  }

}

Output:
a tutorial
ava tutor

Example: Using split and replace

Split is another most commonly used method of String in Java. In this example, we first split the input string using the delimiter ” “. Hence this prints each word separately. Next, we split based on the delimiter but specify limit as 2 which means it splits only into two string array values.

In the 1st example of replacing, we replace the individual character. In the next, we replace the character sequence.

public class StringDemo4 {

  public static void main(String[] args) {
    String str1 = "Welcome to java programming";
    System.out.println("Split output using delimiter:");
    //Split using only delimiter
    String[] arrval = str1.split(" ");
    for(int i=0;i<arrval.length;i++) {
      System.out.println(arrval[i]);
    }
    System.out.println("\nSplit output using delimiter and limit:");
    //Split using delimiter and limit
    String[] arrval2 = str1.split(" ", 2);
    for(int i=0;i<arrval2.length;i++) {
      System.out.println(arrval2[i]);
    }
    
    System.out.println("\nReplace output with character:");
    //Replace character
    String str2 = str1.replace('j', 'J');
    System.out.println(str2);
    System.out.println("\nReplace output with character sequence:");
    String str3 = str1.replace("java", "javascript");
    System.out.println(str3);
  }

}

Output:
Split output using delimiter:
Welcome
to
java
programming

Split output using delimiter and limit:
Welcome
to java programming

Replace output with character:
Welcome to Java programming

Replace output with character sequence:
Welcome to javascript programming

Example: Java Format string

We can format any type of data to a string using the format method. Here, we are using string(“%s”), float(%f”) and boolean(“%b”) as examples.

public class StringFormat {

  public static void main(String[] args) {
    String str = "Java";
    String formatstring1 = String.format("Programming language is %s",str);
    String formatstring2 = String.format("Float value is %f", 55.6789);
    String formatstring3 = String.format("Boolean value is %b", true);
    System.out.println(formatstring1);
    System.out.println(formatstring2);
    System.out.println(formatstring3);
  }

}

Output:
Programming language is Java
Float value is 55.678900
Boolean value is true

Conclusion

In this tutorial, you have learned about String in Java,  different ways of creating it, and different string methods along with examples.

Reference