How Can I Print Doubles in Java with Precise Formatting, Eliminating Unnecessary Trailing Zeros?

Printing Floating Numbers with Precision in Java

Given the ability of a 64-bit double to represent integers precisely within a range, a challenge arises when printing mixed integer and double values. While String.format("%f") provides close formatting, it adds unnecessary trailing zeros for small values.

Seeking a Solution:

The goal is to print integer values stored as doubles without decimal zeros, while maintaining high precision for actual doubles. For instance, given these inputs:

• 232.00000000
• 0.18000000000
• 1237875192.0
• 4.5800000000
• 0.00000000
• 1.23450000

The desired output would be:

• 232
• 0.18
• 1237875192
• 4.58
• 0
• 1.2345

Efficient Formatting:

To optimize formatting, we can exploit the fact that integer values can be represented precisely as 64-bit doubles. The following Java code snippet achieves this without resorting to performance-intensive string manipulation:

public static String fmt(double d) {
    if (d == (long) d)
        return String.format("%d", (long) d);
    else
        return String.format("%s", d);
}

Explanation:

• For integer values that can be accurately represented as doubles, the code converts them to long and formats them using %d. This eliminates unnecessary trailing zeros.
• For non-integer values, the code uses %s to preserve the original double value with minimal precision.

Result:

When applied to the example inputs, the output matches the desired format:

232
0.18
1237875192
4.58
0
1.2345

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