Missing value in Java

Question

What is the statement that can be used in Java to represent a missing value of a variable. for instance I want to write a code:

if (a>=23)
 income = pay_rate;         


        

Answer 1

You can do it following way:

public abstract class Nullable extends Number {

    protected final boolean isNA;


    protected Nullable(boolean isNA) {
        this.isNA = isNA;
    }

    public boolean isNA() {
        return isNA;
    }
}


public final class NullableInt extends Nullable {

    public static final NullableInt NA = new NullableInt(0, true);

    private final int value;

    public NullableInt(int value, boolean isNA) {
        super(isNA);
        this.value = value;
    }

    public static NullableInt of(int value) {
        return new NullableInt(value, false);
    }

    public int getValue() {
        if (!isNA) {
            return value;
        }
        throw new RuntimeException("Value is NA");
    }

    @Override
    public int intValue() {
        return getValue();
    }

    @Override
    public long longValue() {
        return getValue();
    }

    @Override
    public float floatValue() {
        return getValue();
    }

    @Override
    public double doubleValue() {
        return getValue();
    }
}

public class Test {

    public static void main(String[] args) {
        NullableInt[] nullableInts = new NullableInt[3];
        nullableInts[0] = NullableInt.of(1);
        nullableInts[1] = NullableInt.of(2);
        nullableInts[2] = NullableInt.NA;

        System.out.println(Arrays.toString(nullableInts));
    }
}