ComparisonChain

ComparisonChain.java

import java.util.Comparator;

public abstract class ComparisonChain {

    boolean nullValueLess = false;

    public ComparisonChain nullValueLess() {
        nullValueLess = true;
        return this;
    }

    public static ComparisonChain start() {
        return ACTIVE;
    }

    private static final ComparisonChain ACTIVE = new ComparisonChain() {
        @SuppressWarnings("unchecked")
        @Override public ComparisonChain compare(Comparable left, Comparable right) {
            if (nullValueLess) {
                return left == null ?
                        (right == null ? ACTIVE : LESS)
                        :(right == null ? GREATER : classify(left.compareTo(right)));
            } else {
                return classify(left.compareTo(right));
            }
        }
        @Override public <T> ComparisonChain compare(T left, T right, Comparator<T> comparator) {
            if (nullValueLess) {
                return left == null ?
                        (right == null ? ACTIVE : LESS)
                        :(right == null ? GREATER : classify(comparator.compare(left, right)));
            } else {
                return classify(comparator.compare(left, right));
            }
        }
        @Override public ComparisonChain compare(Integer left, Integer right) {
            return compare(left, (Comparable) right);
        }
        @Override public ComparisonChain compare(Long left, Long right) {
            return compare(left, (Comparable) right);
        }
        @Override public ComparisonChain compare(Float left, Float right) {
            return compare(left, (Comparable) right);
        }
        @Override public ComparisonChain compare(Double left, Double right) {
            return compare(left, (Comparable) right);
        }
        @Override public ComparisonChain compareTrueFirst(Boolean left, Boolean right) {
            return compare(right, left); // reversed
        }
        @Override public ComparisonChain compareFalseFirst(Boolean left, Boolean right) {
            return compare(left, right);
        }
        ComparisonChain classify(int result) {
            return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
        }
        @Override public int result() {
            return 0;
        }
    };

    private static final ComparisonChain LESS = new InactiveComparisonChain(-1);

    private static final ComparisonChain GREATER = new InactiveComparisonChain(1);

    private static final class InactiveComparisonChain extends ComparisonChain {
        final int result;

        InactiveComparisonChain(int result) {
            this.result = result;
        }
        @Override public ComparisonChain compare(Comparable left, Comparable right) {
            return this;
        }
        @Override public <T> ComparisonChain compare(T left, T right, Comparator<T> comparator) {
            return this;
        }
        @Override public ComparisonChain compare(Integer left, Integer right) {
            return this;
        }
        @Override public ComparisonChain compare(Long left, Long right) {
            return this;
        }
        @Override public ComparisonChain compare(Float left, Float right) {
            return this;
        }
        @Override public ComparisonChain compare(Double left, Double right) {
            return this;
        }
        @Override public ComparisonChain compareTrueFirst(Boolean left, Boolean right) {
            return this;
        }
        @Override public ComparisonChain compareFalseFirst(Boolean left, Boolean right) {
            return this;
        }
        @Override public int result() {
            return result;
        }
    }

    public abstract ComparisonChain compare(Comparable<?> left, Comparable<?> right);

    public abstract <T> ComparisonChain compare(T left, T right, Comparator<T> comparator);

    public abstract ComparisonChain compare(Integer left, Integer right);

    public abstract ComparisonChain compare(Long left, Long right);

    public abstract ComparisonChain compare(Float left, Float right);

    public abstract ComparisonChain compare(Double left, Double right);

    public abstract ComparisonChain compareTrueFirst(Boolean left, Boolean right);

    public abstract ComparisonChain compareFalseFirst(Boolean left, Boolean right);

    public abstract int result();
}