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The Checker Framework enhances Java's type system to make it more powerful and useful. This lets software developers detect and prevent errors in their Java programs. The Checker Framework includes compiler plug-ins ("checkers") that find bugs or verify their absence. It also permits you to write your own compiler plug-ins.

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package org.checkerframework.checker.guieffect;

import org.checkerframework.checker.guieffect.qual.PolyUIEffect;
import org.checkerframework.checker.guieffect.qual.SafeEffect;
import org.checkerframework.checker.guieffect.qual.UIEffect;
import org.checkerframework.checker.nullness.qual.Nullable;
import org.checkerframework.dataflow.qual.Pure;
import org.checkerframework.dataflow.qual.SideEffectFree;

import java.lang.annotation.Annotation;

/** An effect -- either UIEffect, PolyUIEffect, or SafeEffect. */
public final class Effect {
    // Colin hates Java's comparable interface, so he's not using it

    private final Class annotClass;

    /**
     * Create a new Effect object.
     *
     * @param cls one of UIEffect.class, PolyUIEffect.class, or SafeEffect.class
     */
    public Effect(Class cls) {
        assert cls == UIEffect.class || cls == PolyUIEffect.class || cls == SafeEffect.class;
        annotClass = cls;
    }

    /**
     * Return true iff {@code left} is less than or equal to {@code right}.
     *
     * @param left the first effect to compare
     * @param right the first effect to compare
     * @return true iff {@code left} is less than or equal to {@code right}
     */
    public static boolean lessThanOrEqualTo(Effect left, Effect right) {
        assert (left != null && right != null);
        boolean leftBottom = left.annotClass == SafeEffect.class;
        boolean rightTop = right.annotClass == UIEffect.class;
        return leftBottom || rightTop || left.annotClass == right.annotClass;
    }

    public static Effect min(Effect l, Effect r) {
        if (lessThanOrEqualTo(l, r)) {
            return l;
        } else {
            return r;
        }
    }

    public static final class EffectRange {
        public final Effect min;
        public final Effect max;

        public EffectRange(@Nullable Effect min, @Nullable Effect max) {
            assert (min != null || max != null);
            // If one is null, fill in with the other
            this.min = (min != null ? min : max);
            this.max = (max != null ? max : min);
        }
    }

    /**
     * Return true if this is SafeEffect.
     *
     * @return true if this is SafeEffect
     */
    public boolean isSafe() {
        return annotClass == SafeEffect.class;
    }

    /**
     * Return true if this is UIEffect.
     *
     * @return true if this is UIEffect
     */
    public boolean isUI() {
        return annotClass == UIEffect.class;
    }

    /**
     * Return true if this is PolyUIEffect.
     *
     * @return true if this is PolyUIEffect
     */
    @Pure
    public boolean isPoly() {
        return annotClass == PolyUIEffect.class;
    }

    public Class getAnnot() {
        return annotClass;
    }

    @SideEffectFree
    @Override
    public String toString() {
        return annotClass.getSimpleName();
    }

    /**
     * Return true if this equals the given effect.
     *
     * @param e the effect to compare this to
     * @return true if this equals the given effect
     */
    @SuppressWarnings("NonOverridingEquals") // TODO: clean this up!
    public boolean equals(Effect e) {
        return annotClass == e.annotClass;
    }

    @Override
    @SuppressWarnings("interning:not.interned") // equality
    public boolean equals(@Nullable Object o) {
        if (o instanceof Effect) {
            return this.equals((Effect) o);
        } else {
            return this == o;
        }
    }

    @Pure
    @Override
    public int hashCode() {
        return 31 + annotClass.hashCode();
    }
}