Common Errors with Datatypes

1. Loss of Precision

When converting from a larger data type to a smaller one (like double → int or float → int), some part of the data may be lost. This usually happens when decimals are truncated during conversion.

Example:

public class PrecisionLoss {
    public static void main(String[] args) {
        double value = 12.99;
        int num = (int) value;  // Explicit casting (double → int)
        System.out.println("Original value: " + value);
        System.out.println("After conversion: " + num);
    }
}

2. Overflow and Underflow

When a variable stores a value beyond its range, it causes overflow (too large) or underflow (too small). Java does not throw an error but instead wraps around to the other end of the range.

Example:

public class OverflowExample {
    public static void main(String[] args) {
        int max = Integer.MAX_VALUE;
        int result = max + 1;  // Overflow
        System.out.println("Max value: " + max);
        System.out.println("After overflow: " + result);
    }
}

3. NullPointerException

This occurs when you try to access a method or property of an object that is null (i.e., not initialized). It’s a common error when working with non-primitive (reference) types.

Example:

public class NullPointerError {
    public static void main(String[] args) {
        String text = null;
        System.out.println(text.length()); // Error: NullPointerException
    }
}

Always check for null before using an object:

if (text != null) {
    System.out.println(text.length());
}

Summary: