Java Program to convert a String to int


To convert a String to int in Java, we can use the two built-in methods namely parseInt() and valueOf(). These static methods belong to the Integer class of java.lang package and throws a NumberFormatException if the string is not a valid representation of an integer. In Java, String is a class of 'java.lang' package that stores a series of characters enclosed within double quotes. And, an integer is a primitive datatype that stores numerical values. In this article, we will discuss a few Java programs that illustrate how to convert a given String to integer.

Java Program to Convert a String to int

As mentioned earlier, we will use the following methods to convert a string into an integer −

  • Integer.parseInt()

  • Integer.valueOf()

Let's discuss these methods one by one with the help of example programs.

Using Integer.parseInt()

The Integer.parseInt() method takes a string as a parameter and parses it into a primitive integer value.

Syntax

Integer.parseInt(String val);

Example 

The following Java program demonstrates how to convert a String into int using the parseInt() method.

Approach

  • Initialize a string which will be converted to integer.

  • Next, check and print the type of defined string using the getClass() and getSimpleName() methods.

  • Now, convert the string into integer using parseInt() method and store the result in an integer variable.

  • In the end, check and print the datatype to confirm whether the string is converted into integer or not.

public class Example1 {
   public static void main( String args[] ) {
      // initializing a string
      String inputString = "99999";
      // to check the datatype of string 
      System.out.print("Type of inputString: ");
      System.out.println(inputString.getClass().getSimpleName());
      // converting the string into an integer
      int newVal = Integer.parseInt(inputString);
      // printing the result
      System.out.println("The given String after converting into Integer: " + newVal);
      // to check the datatype of integer 
      System.out.print("Type of given String after converting into Integer: ");
      System.out.println(((Object)newVal).getClass().getSimpleName());
   }
}

Output

Type of inputString: String
The given String after converting into Integer: 99999
Type of given String after converting into Integer: Integer

Using Integer.valueOf()

The Integer.valueOf() method can take a string, a char or an int as a parameter but returns an Integer object that holds the value of the parsed integer.

Syntax

Integer.valueOf(String val);

Example  1

This is another Java program that will show how we can convert a String into int with the help of Integer.valueOf() method.

public class Example2 {
   public static void main( String args[] ) {
      // initializing a string
      String inputString = "30072023";
      // to check the datatype of string 
      System.out.print("Type of inputString: ");
      System.out.println(inputString.getClass().getSimpleName());
      // converting the string into an integer
      int newVal = Integer.valueOf(inputString);
      // printing the result
      System.out.println("The given String after converting into Integer: " + newVal);
      // to check the datatype of integer 
      System.out.print("Type of given String after converting into Integer: ");
      System.out.println(((Object)newVal).getClass().getSimpleName());
   }
}

Output

Type of inputString: String
The given String after converting into Integer: 30072023
Type of given String after converting into Integer: Integer

Example 2

Earlier we mentioned that the parseInt() and valueOf() methods throw a NumberFormatException if the passed string is not a valid representation of an integer. In this Java program, we will pass a string with alphabetical characters instead of numerical characters to show the exception.

public class Example3 {
   public static void main( String args[] ) {
      // initializing a string
      String inputString = "TutorialsPoint";
      // converting the string to the integer
      int newVal = Integer.valueOf(inputString); // will give exception
      // printing the result
      System.out.println("The given String after converting into Integer: " + newVal);
   }
}

Output

Exception in thread "main" java.lang.NumberFormatException: For input string: "TutorialsPoint"
at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
at java.base/java.lang.Integer.parseInt(Integer.java:665)
at java.base/java.lang.Integer.valueOf(Integer.java:992)
at Example3.main(Example3.java:6)

Conclusion

Both Integer.parseInt() and Integer.valueOf() are very useful methods for converting strings to integers. But, the performance of Integer.valueOf() method is significantly faster than Integer.parseInt() method. We have discussed three Java programs that illustrate the practical implementation of these methods.

karthikeya Boyini
karthikeya Boyini

I love programming (: That's all I know

Updated on: 10-Aug-2023

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