How to easily Convert String to Integer in JAVA

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()

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"