String class methods in Java

In the previous tutorial, we learned about the Exception Handling in Java with examples. In this tutorial, we will learn about String class methods in Java.

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In Java, a String is a pre-defined class that is present in java.lang package. This class is final which implies that no class can extend this. The string class is also immutable. This means that once created and initialized, cannot be changed on the same reference.

Now, we will learn how to create the object of the string class in java

String Class Methods in Java with detailed examples
String Class Methods in Java with detailed examples

Creating String Class Object

A simple String is created using the string literal enclosed between double quotes. An example of this is shown below :

String s = “My Name is James”;

One of the important points about String is that, if more than one same set of characters with the same sequence has been assigned to a different string, then they share the same reference in the memory.

Example –

String s1 = “My Name is James”;

String s2 = “My Name is James”;

String s3 = “My Name” + “is James”;

In this, all the string references s1, s2 and s3 denote the same String object.

One more way of creating the string is with the help of a new keyword. But, in this case, even if the same set of characters with the same sequence is passed, a new reference is created.

Syntax –

String s5 = new String(“My Name is James”);

Concatenation Operator

In Java, String objects can be used with the += and + operators for concatenation. In the concatenation operator, to concatenate between two objects, one of them must be a string and the other can be any.

Given below, is a simple program based on the string operators –

Class Example{
Public static void main(String[] args){
String s1 = “computer”;
String s2 = “computer”;
String s3 = new String(“computer”);
System.out.println(“Result 1”+(s1 == s2));
System.out.println(“Result 2”+(s1.equals(s2));
System.out.println(“Result 3”+(s1 == s3));
System.out.println(“Result 4”+s1.equals(s3));
}
}

Output –

True
True
False
True

String class methods in Java

Case Conversion

toUpperCase()

toLowerCase()

We will understand these with the example given below –

public class Example{
public static void main(String args[]){
String s1 = new String(“hello world”);
System.out.println(s1);
S1.toUpperCase();
System.out.println(s1);
S1.toLowerCase();
System.out.println(s1);
}
}

Output –

hello world

HELLO WORLD

Hello world

Indexof() method –

public class Example{
public static void main(String[] args){
String s1 = new String(“Computer”);
int i = s1.indexOf(‘m’);
System.out.println(“Index is “+ i);
}
}

Output –

3

Some other versions of IndexOf() functions are –

indexOf(int ch) – To search the index of a character in a String

indexOf(int ch, int fromIndex) – To search the index of a character from a specific position

indexOf(String str) – To search the position of a substring in a string

indexOf(String str, int fromIndex) – To search the position of a substring from a specific position

lastIndexOf(int ch) – To search the index of a character from last of the string

lastIndexOf(int ch, int fromIndex) – To search the index of a character from the last and a specific position

lastIndexOf(String str) -To search the index of a substring from last

lastIndexOf(String str, int fromIndex) – To search the index of a substring from the last and from a specific position

Comparing Strings

Two String can be compared using the equals function. The functions used to compare strings are given below –

equals()
public class Example{
public static void main(String[] args){
String s1 = new String(“Process”);
String s2 = new String(“process”);
if(s1.equals(s2)) System.out.println(“They are equal”);
else System.out.println(“They are not equal”);}}

Output –

They are not equal

Explanation –

The strings will not be considered equal because of the difference in the first character.

But, if we use the equalsIgnoreCase() method in java, the comparison is case insensitive. Thus, this will return true.

Example –

public class Example{
public static void main(String[] args){
String s1 = new String(“Process”);
String s2 = new String(“process”);
if(s1.equalsIgnoreCase(s2)) System.out.println(“They are equal”);
else
 System.out.println(“They are not equal”);}}

Similarly, there is one more version of the compare method, which is Compareto() method. We will understand this with the help of the example given below –

public class Example{
public static void main(String[] args){
String s1 = new String(“Process”);
String s2 = new String(“process”);
int i = s1.compareTo(s2));
if(i == 0) 
 System.out.println(“Strings are equal”);
else if(i>0)
 System.out.println(“They are opposite to dictionary order”);}}
else
System.out.prinln(“Dictionary Order”);

Split Method()

This method divides the string and returns an array of substrings.

Example –

class Main {

  public static void main(String[] args) {

    String text = "We are learning to program in Java";

    String[] result = text.split(" ");

    System.out.print("result = ");

    for (String str : result) {

      System.out.print(str + ", ");

    }

  }}

Output –

Result = We, are, learning, to, program, in, Java

length() Method

This method returns the length of the string.

Example –

Class Main {

  public static void main(String[] args) {

      String str1 = “Java is fun”;

      System.out.println(str1.length());

  }}

Output –

11

Replace() Method

This method replaces each matching occurrence of the old character with the new one.

Example  –

class Main {

  public static void main(String[] args) {

    String str1 = "bat ball";

    System.out.println(str1.replace('b', 'h'));

  }

}

Output –

Hat hall

Substring() Method

This method extracts a substring from a string and returns it.

Example –

class Main {

  public static void main(String[] args) {

    String str1 = “java is fun”;

    System.out.println(str1.substring(0, 4));

  }

}

Output –

 Java

isEmpty() Method

This method checks whether the string is empty or not.

Example –

class Main {

  public static void main(String[] args) {

    String str1 = "Java Programming";

    String str2 = "";

    System.out.println(str1.isEmpty()); 

    System.out.println(str2.isEmpty()); 

  }

}

Output –

False

True

String toCharArray() method

This method converts the string to array of char, and returns it.

Example – 

class Main {

  public static void main(String[] args) {

    String str = "Java Programming";

    char[] result;

    result = str.toCharArray();

    System.out.println(result);

  }

}

Output –

Java Programming

So, in this article, we learned about the String and String methods used in them in detail.

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