public class DecimalToLongProgram {
/**
============================================================
Convert decimal-like values to long in Java.
This class demonstrates:
• Conversion using Math.round() for floating-point rounding.
• Conversion using a direct cast (long) for truncation.
• Conversion using BigDecimal.longValue() and longValueExact().
• A helper method that prints all conversion styles.
Notes:
• Math.round() returns a long and rounds to nearest integer.
• (long)value truncates the fractional part.
• BigDecimal.longValue() truncates.
• BigDecimal.longValueExact() throws if fractional or out of range.
============================================================
*/
// Rounds a double to long
static long convertDoubleToLong(double value) {
return Math.round(value);
}
// Truncates a double to long
static long castDoubleToLong(double value) {
return (long) value;
}
// Rounds or truncates a BigDecimal
static long convertBigDecimalToLong(java.math.BigDecimal value) {
return value.longValue(); // truncates
}
// Exact conversion (throws if fractional)
static long convertBigDecimalExact(java.math.BigDecimal value) {
return value.longValueExact(); // strict
}
// Prints all conversion styles for comparison
static void showConversions(double value) {
System.out.println("Input decimal (double): " + value);
long rounded = convertDoubleToLong(value);
long truncated = castDoubleToLong(value);
System.out.println("Rounded (Math.round): " + rounded);
System.out.println("Truncated (cast to long): " + truncated);
System.out.println();
}
static void showConversions(java.math.BigDecimal value) {
System.out.println("Input decimal (BigDecimal): " + value);
long truncated = convertBigDecimalToLong(value);
System.out.println("Truncated (longValue): " + truncated);
try {
long exact = convertBigDecimalExact(value);
System.out.println("Exact (longValueExact): " + exact);
} catch (ArithmeticException ex) {
System.out.println("Exact (longValueExact): ERROR — fractional or out of range");
}
System.out.println();
}
public static void main(String[] args) {
// Floating-point examples
showConversions(12.7);
showConversions(12.3);
showConversions(-5.8);
showConversions(42.0);
// BigDecimal examples
// it only succeeds when the BigDecimal represents a whole number that fits inside a long.
showConversions(new java.math.BigDecimal("12.7"));
showConversions(new java.math.BigDecimal("42"));
showConversions(new java.math.BigDecimal("-5.8"));
}
}
/*
run:
Input decimal (double): 12.7
Rounded (Math.round): 13
Truncated (cast to long): 12
Input decimal (double): 12.3
Rounded (Math.round): 12
Truncated (cast to long): 12
Input decimal (double): -5.8
Rounded (Math.round): -6
Truncated (cast to long): -5
Input decimal (double): 42.0
Rounded (Math.round): 42
Truncated (cast to long): 42
Input decimal (BigDecimal): 12.7
Truncated (longValue): 12
Exact (longValueExact): ERROR ? fractional or out of range
Input decimal (BigDecimal): 42
Truncated (longValue): 42
Exact (longValueExact): 42
Input decimal (BigDecimal): -5.8
Truncated (longValue): -5
Exact (longValueExact): ERROR ? fractional or out of range
*/
