Java – Parse integer from string containing letters

This post shows you how to parse a string containing letters to an integer using Java.

1. First case: We only want to get an integer from the first digits of the string

To do this, we need to use NumberFormat class to parse a string to an integer. Here is the code example:

package com.bytenota;

import java.text.NumberFormat;
import java.text.ParseException;

public class StringExample {
    
    public static void main(String[] args) throws ParseException {
        String str1 = "123abcd";
        int result1 = NumberFormat.getInstance().parse(str1).intValue();
        System.out.println(result1); // 123
        
        String str2 = "20.4fcdw31";
        int result2 = NumberFormat.getInstance().parse(str2).intValue();
        System.out.println(result2); // 20
        
        String str3 = "15ab23";
        int result3 = NumberFormat.getInstance().parse(str3).intValue();
        System.out.println(result3); // 15
    }
}

2. Second case: We want to get an integer from the digits of the string

We simply remove all non-digit characters from the string and then parse it to integer using Integer.parseInt method as normal. Here is the code example:

package com.bytenota;

import java.text.ParseException;

public class StringExample {
    
    public static void main(String[] args) throws ParseException {
        String str1 = "123abcd";
        int result1 = Integer.parseInt(str1.replaceAll("\\D", ""));
        System.out.println(result1); // 123
        
        String str2 = "20.4fcdw31";
        int result2 = Integer.parseInt(str2.replaceAll("\\D", ""));
        System.out.println(result2); // 20431
        
        String str3 = "15ab23";
        int result3 = Integer.parseInt(str3.replaceAll("\\D", ""));
        System.out.println(result3); // 1523
    }
}