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There are two ways to convert String to Integer in Java,

  1. String to Integer using Integer.parseInt()
  2. String to Integer using Integer.valueOf()
How to convert a Java String to Integer?

Let’s say you have a string – strTest - that contains a numeric value.
String strTest = “100”;
Try to perform some arithmetic operation like divide by 4 – This immediately shows you a compilation error.
class StrConvert{
  public static void main(String []args){
    String strTest = "100";
    System.out.println("Using String:" + (strTest/4));
  }
}

Output:

/StrConvert.java:4: error: bad operand types for binary operator '/'
    System.out.println("Using String:" + (strTest/4));

Hence, you need to convert a String to int before you peform numeric operations on it

Example 1: Convert String to Integer using Integer.parseInt()


Syntax of parseInt method as follows:
int <IntVariableName> = Integer.parseInt(<StringVariableName>);

Pass the string variable as the argument.

This will convert the Java String to java Integer and store it into the specified integer variable.

Check the below code snippet-

class StrConvert{
  public static void main(String []args){
    String strTest = "100";
    int iTest = Integer.parseInt(strTest);
    System.out.println("Actual String:"+ strTest);
    System.out.println("Converted to Int:" + iTest);
    //This will now show some arithmetic operation
    System.out.println("Arithmetic Operation on Int: " + (iTest/4));
  }
}

Output:

Actual String:100
Converted to Int:100
Arithmetic Operation on Int: 25

Example 2: Convert String to Integer using Integer.valueOf()

Integer.valueOf() Method is also used to convert String to Integer in Java.

Following is the code example shows the process of using Integer.valueOf() method:

public class StrConvert{
  public static void main(String []args){
    String strTest = "100";
    //Convert the String to Integer using Integer.valueOf
    int iTest = Integer.valueOf(strTest);
    System.out.println("Actual String:"+ strTest);
    System.out.println("Converted to Int:" + iTest);
    //This will now show some arithmetic operation
    System.out.println("Arithmetic Operation on Int:" + (iTest/4));
  }
}

Output:

Actual String:100
Converted to Int:100
Arithmetic Operation on Int:25

NumberFormatException

NumberFormatException is thrown If you try to parse an invalid number string. For example, String ‘Guru99’ cannot be converted into Integer.

Example:

public class StrConvert{
  public static void main(String []args){
    String strTest = "Guru99";
    int iTest = Integer.valueOf(strTest);
    System.out.println("Actual String:"+ strTest);
    System.out.println("Converted to Int:" + iTest);
  }
}

Above example gives following exception in output:

Exception in thread "main" java.lang.NumberFormatException: For input string: "Guru99"

 

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