Converting Between `long` and `String` in Java: A Comprehensive Tutorial

Introduction

In Java, working with different data types is a common task. Converting between primitive data types like long and objects like String can be essential when dealing with user input, databases, or APIs. This tutorial will guide you through converting a long to a String and vice versa, ensuring you understand the methods and best practices in Java.

Understanding Data Types

• long: A primitive data type representing 64-bit signed integers.
• String: An object that represents sequences of characters.

Converting between these types is straightforward but requires understanding the appropriate methods provided by Java.

Converting long to String

There are several ways to convert a long value to a String. Here are some common methods:

1. Using Long.toString(long)

This method directly converts a long to its String representation.

long date = 1627849200000L;
String str = Long.toString(date);
System.out.println(str); // Outputs: "1627849200000"

2. Using String.valueOf(long)

This static method from the String class provides a simple conversion.

long date = 1627849200000L;
String str = String.valueOf(date);
System.out.println(str); // Outputs: "1627849200000"

3. Concatenation with an Empty String

By concatenating a long with an empty string, Java automatically converts it to String.

long date = 1627849200000L;
String str = "" + date;
System.out.println(str); // Outputs: "1627849200000"

Converting String to long

To convert a String back to a long, use the following methods:

1. Using Long.valueOf(String)

This method parses the string as a long. It throws a NumberFormatException if the string is not a valid representation of a long.

String str = "1627849200000";
try {
    long date = Long.valueOf(str);
    System.out.println(date); // Outputs: 1627849200000
} catch (NumberFormatException e) {
    System.err.println("Invalid input for conversion to long.");
}

2. Using Long.parseLong(String)

Similar to Long.valueOf, this method parses the string and throws a NumberFormatException on invalid input.

String str = "1627849200000";
try {
    long date = Long.parseLong(str);
    System.out.println(date); // Outputs: 1627849200000
} catch (NumberFormatException e) {
    System.err.println("Invalid input for conversion to long.");
}

Best Practices

• Error Handling: Always handle potential NumberFormatException when converting from String to long.
• Null Safety: If there’s a possibility of null values, use Objects.toString(obj, defaultValue) to avoid exceptions.
• Code Readability: Choose the method that best fits your code style and readability needs. For example, String.valueOf() is often preferred for its simplicity.

Conclusion

Converting between long and String in Java is a fundamental skill that can be accomplished using several methods. Understanding these conversions ensures robust and error-free data handling in your applications. Whether you’re logging timestamps, storing values in a database, or interacting with user input, mastering these conversions will enhance your Java programming capabilities.