How to Convert String into Integer in Java:

We can convert String into Integer Using three methods namely Integer.parseInt(), Integer.ValueOf(), and the tryParse Methods.

The Conversion of String to Integer is used in Java when we want to do the Mathematical operations.

Generally, the input is taken in the form of a string in java.

If the input string is number then in such cases there should be a method to convert String into Integer.

So in this lesson, we will see How to Convert String into Integer in Java using different Methods with Explanation one by one.

## 1. How to Convert String into Integer in Java Using Integer.parseInt() Method

In this program, we will make use of java inbuilt method called as Integer.parseInt() method. So, first of all

What is Integer.parseInt() Method?

Generally, Integer.parseInt() is a java inbuilt method which is used to convert the input string in the form of an integer.

Syntax: Integer.parseInt()

For Example: str=”12345″; int j=Integer.parseInt(str);

After executing the example line in the program we will get the output as 12345.

If the Input String is not valid then the program throws the Exception called NumberFormatException.

So let us see how to write a program to convert string to integer in java using Integer.parseInt() method.

```//Learnprogramo
public class Main
{
public static void main(String args[])
{
//Declaring String variable
String s="575";
//Converting String into int using Integer.parseInt()
int j=Integer.parseInt(s);
//Printing value of i
System.out.println(j);
}
}  ```

Output:

In the above program, we have given input as 575 and store it in String variable s.

Integer.parseInt(s) converts the string into an Integer Hence we get the output as Integer i.e 575.

## 2. How to Convert String into Integer in Java Using Integer.valueOf() Method

So, before start learning, we will do a quick overview of inbuilt java method called as Integer.valueOf(). So

What is Integer.valueOf() Method in Java?

This inbuilt java method is used to converting the string value in the integer.

This method returns the integer object which holds the value in the form of string.

Syntax: Integer.valueOf(s).

For Example: String s=”12345″; int j=Integer.valueOf(s);

In the above example, we have given input string as 12345 and stored it in s.

By using method Integer.valueOf(s) the string value 12345 is converted into an integer.

```//Learnprogramo
public class Main
{
public static void main(String args[])
{
//Declaring a string
String s="12345";
//converting String into Integer using Integer.valueOf() method
Integer j=Integer.valueOf(s);
System.out.println(j);
}
}  ```

Output:

## 3. Using Ints::tryParse Method of Guava Library

This method is of Guava Library which is similar to Integer.parseInt() method and is more powerful than other methods.

So let us see the conversion of a string into an integer in java using tryParse method of Guava Library.

```//Learnprogramo
import java.io.*;
import java.util.*;
public class Main {
// Function to convert String to integer
public static int convert(String str)
{
int val = 0;
System.out.println("String = " + str);
// Convert the String
val = Optional.ofNullable(str)
.map(Ints::tryParse)
.orElse(0);
return val;
}
//main
public static void main(String[] args)
{
String str = "1234";
int val = convert(str);
System.out.println("Integer value = " + val);
System.out.println();
str = "123s";
val = convert(str);
System.out.println("Integer value = " + val);
}
} ```

Output:

## 4. NumberFormatException

The NumberFormatException is a type of Exception in java which mainly arises when the input string is invalid.

For Example “programo123” cannot be converted into the integer because the input string is invalid which contains string as well as integers.

So let us see how the NumberFormatException arises in java during the execution of the program.

```//Learnprogramo
public class Main
{
public static void main(String args[])
{
String s="programo123";
int j=Integer.parseInt(s);
System.out.println(j);
}
}  ```

Output:

## 5. How to Convert String into Integer in Java with leading zeros

consider a string which contains all the integer values with leading zeros. So to perform an arithmetic operation on that string which retains the leading zeros we will need to first convert the string into an integer.

After we will use format() method to convert the output value into the string.

```//Learnprogramo
public class Main
{
public static void main(String args[])
{
String str="00000575";
/* String to int conversion with leading zeroes
* the %08 format specifier is used to have 8 digits in
* the number, this ensures the leading zeroes
*/
str = String.format("%08d", Integer.parseInt(str)+102);
System.out.println("Output String: "+str);
}
}```

Output: