Convert String to double in Java

Input sanitation: Cleanse before you parse

Before attempting conversion, validate the format of the input string. This measure guards against NumberFormatException, saving you from unexpected bugs.

String input = "123.45";
if (input != null && input.matches("-?\\d+(\\.\\d+)?")) {
    double value = Double.parseDouble(input); // Pvt. Input reporting for duty, Sir!
} else {
    System.err.println("Invalid input string"); // Pvt. Input failed the inspection, Sir!
}
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The regex -?\\d+(\\.\\d+)? checks for an optional negative sign, a sequence of digits, and optionally a decimal fraction part.

Locale gotchas: Lost in translation

Locale-dependent decimal separators can trigger parsing errors. Some regions use , instead of ..

String euroInput = "123,45";
euroInput = euroInput.replace(',', '.'); // Lost in translation? Not on my watch
double value = Double.parseDouble(euroInput);
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By replacing , with ., we present a locale-independent decimal separator to the parser.

Monetary value: A penny for your thoughts

When dealing with financial operations, leverage the BigDecimal class for its unparalleled precision:

String financialStr = "123.45678";
BigDecimal financialVal = new BigDecimal(financialStr); // When accuracy is worth its weight in gold
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BigDecimal maintains precision during conversion, ensuring accurate results for financial calculations - No one likes to lose pennies, right?

An alternate turn: There's more than one way to skin a cat

You may use Double.valueOf(String s), which returns a Double object rather than a primitive double:

Double numberObject = Double.valueOf("123.45"); // I'm double, not a single
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Unbox the Double object if a primitive double value is required:

double numberPrimitive = numberObject.doubleValue(); // Can't box me up
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Large data scenario: Big data, big responsibilities

When dealing with large-scale data processing, efficiency is paramount for maintaining overall performance:

• Use conditional checks for early-phase invalid string filtration.
• Cache parsed values that appear frequently. Why do the same work twice?
• Perform regular performance profiling to identify and optimize potential bottlenecks. It's like a health check-up for your program!

Fall like a cat: Always land on your feet

Investing in error handling leads to improved data integrity and robustness:

String input = "not a number";
try {
    double value = Double.parseDouble(input);
} catch (NumberFormatException e) {
    System.err.println("Caught NumberFormatException: It's a string not a number, silly!"); // Whoa, cowboy! Easy there.
}
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In this way, your program can gracefully recover from errors and provide meaningful feedback to its users.

Accuracy in action: Measure twice, cut once

Ensure the input string accurately represents a double:

String piRepresentation = "3.1415926535";
double pi = Double.parseDouble(piRepresentation); // I see Pi!
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The string must be in the correct format to be correctly parsed into a double. Set your standards right!