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Common reflection code used in support of annotation processing

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package org.hibernate.annotations.common.reflection.java;

/**
 * A pair of objects that can be used as a key in a Map.
 *
 * @author Paolo Perrotta
 * @author Davide Marchignoli
 */
abstract class Pair {

	private final T o1;

	private final U o2;
    private final int hashCode;

    Pair(T o1, U o2) {
		this.o1 = o1;
		this.o2 = o2;
        this.hashCode = doHashCode();
    }

	@Override
	public boolean equals(Object obj) {
		if ( ! (obj instanceof Pair) ) {
			 return false;
		}
		Pair other = (Pair) obj;
        return !differentHashCode( other ) && safeEquals( o1, other.o1 ) && safeEquals( o2, other.o2 );
    }

    private boolean differentHashCode(Pair other) {
        return hashCode != other.hashCode;
    }

    @Override
	public int hashCode() {
        //cached because the inheritance can be big
        return hashCode;
	}

    private int doHashCode() {
		return safeHashCode( o1 ) ^ safeHashCode( o2 );
	}

	private int safeHashCode(Object o) {
		if ( o == null ) {
			return 0;
		}
		return o.hashCode();
	}

	private boolean safeEquals(Object obj1, Object obj2) {
		if ( obj1 == null ) {
			return obj2 == null;
		}
        return obj1.equals( obj2 );
	}
}