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Java Dictionary

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Integer.parseInt() / Double.parseDouble()

Integer.parseInt() / Double.parseDouble()

A method that converts a numeric string into a numeric type that can be used in calculations. Use it when you need to treat values read from user input or files as numbers. If a string that cannot be converted is passed, an exception is thrown.

Syntax

// Converts a string to int.
int variableName = Integer.parseInt(string);

// Converts a string to double.
double variableName = Double.parseDouble(string);

// Converts a string to float.
float variableName = Float.parseFloat(string);

// Converts a string to long.
long variableName = Long.parseLong(string);

Method List

Method	Description
Integer.parseInt(String s)	Converts a string to an `int` value. Throws `NumberFormatException` if the string cannot be converted.
Double.parseDouble(String s)	Converts a string to a `double` value.
Float.parseFloat(String s)	Converts a string to a `float` value.
Long.parseLong(String s)	Converts a string to a `long` value.

Sample Code

// Converts a string to int.
String numStr = "42";
int num = Integer.parseInt(numStr);
System.out.println(num + 10); // Prints "52".

// Converts a string to double.
String priceStr = "3.14";
double price = Double.parseDouble(priceStr);
System.out.println(price * 2); // Prints "6.28".

// Converts a string to long (for large numbers).
String bigStr = "9999999999";
long big = Long.parseLong(bigStr);
System.out.println(big); // Prints "9999999999".

// A string that cannot be converted throws an exception.
try {
    int invalid = Integer.parseInt("abc"); // Throws NumberFormatException.
} catch (NumberFormatException e) {
    System.out.println("Cannot convert: " + e.getMessage());
}

// To convert a number to a string (the reverse), use String.valueOf().
int value = 100;
String str = String.valueOf(value);
System.out.println(str.getClass().getSimpleName()); // Prints "String".

Notes

Parse methods such as parseInt() throw a NumberFormatException if the string cannot be converted (e.g., alphabetic characters, empty strings, or strings containing only spaces). When converting uncertain values such as user input, handle the exception with a try-catch block.

The two-argument form Integer.parseInt(string, radix) lets you convert binary, octal, or hexadecimal strings to decimal (e.g., Integer.parseInt("FF", 16) returns 255).

For integer constants and base conversion, see Integer.MAX_VALUE / MIN_VALUE / toBinaryString().

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