Given String str containing digits as characters, the task is to convert this given string to integer in Java.

Examples:

Input: str = "1234"
Output: 1234

Input: str = "213s"
Output: 0
Since the String contains other than digits,
hence the integer value will be 0

• Method 1: Use Integer.parseInt() method
  This is the most simple method to convert String to integer. This function parses the string argument as a signed decimal integer.

  Syntax:

  public static int parseInt(String s)
              throws NumberFormatException
  

  Below is the implementation of the above approach:

  
  
  
  
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  // Java program to convert String to int // using Integer.parseInt() method    import java.io.*;    class GFG {        // Function to convert String to integer     public static int convert(String str)     {         int val = 0;         System.out.println("String = " + str);            // Convert the String         try {             val = Integer.parseInt(str);         }         catch (NumberFormatException e) {                // This is thrown when the String             // contains characters other than digits             System.out.println("Invalid String");         }         return val;     }        // Driver code     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);     } }

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  Output:

  String = 1234
  Integer value = 1234
  
  String = 123s
  Invalid String
  Integer value = 0
  

• Method 2: Use Ints::tryParse method of Guava library
  Another method to convert String to integer is to use Ints::tryParse method of Guava library. It is similar to the Integer.parseInt() method, but this method is more concise and powerful.

  Syntax:

  public static Integer tryParse(String s)
  

  Below is the implementation of the above approach:

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  // Java program to convert String to int // using Ints::tryParse method    import java.io.*; import java.util.*; import com.google.common.primitives.Ints;    class GFG {        // 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;     }        // Driver code     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);     } }

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  Output:

  String = 1234
  Integer value = 1234
  
  String = 123s
  Integer value = 0
  

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