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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.dataflow.cfg.node;

import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.MemberSelectTree;
import com.sun.source.tree.Tree;

import org.checkerframework.checker.nullness.qual.Nullable;
import org.checkerframework.dataflow.qual.SideEffectFree;
import org.checkerframework.javacutil.BugInCF;
import org.checkerframework.javacutil.TreeUtils;

import java.util.Collection;
import java.util.Collections;
import java.util.Objects;

import javax.lang.model.element.PackageElement;

/**
 * A node representing a package name used in an expression such as a constructor invocation.
 *
 * package.class.object(...)
 *
 * parent.package.class.object(...)
 */
public class PackageNameNode extends Node {

    /** The package name, which is an IdentifierTree or a MemberSelectTree. */
    protected final Tree tree;

    /** The package named by this node. */
    protected final PackageElement element;

    /** The parent name, if any. */
    protected final @Nullable PackageNameNode parent;

    public PackageNameNode(IdentifierTree tree) {
        super(TreeUtils.typeOf(tree));
        this.tree = tree;
        assert TreeUtils.isUseOfElement(tree) : "@AssumeAssertion(nullness): tree kind";
        PackageElement element = (PackageElement) TreeUtils.elementFromUse(tree);
        if (element == null) {
            throw new BugInCF("null element for %s [%s]", tree, tree.getClass());
        }
        this.element = element;
        this.parent = null;
    }

    public PackageNameNode(MemberSelectTree tree, PackageNameNode parent) {
        super(TreeUtils.typeOf(tree));
        this.tree = tree;
        assert TreeUtils.isUseOfElement(tree) : "@AssumeAssertion(nullness): tree kind";
        PackageElement element = (PackageElement) TreeUtils.elementFromUse(tree);
        if (element == null) {
            throw new BugInCF("null element for %s [%s]", tree, tree.getClass());
        }
        this.element = element;
        this.parent = parent;
    }

    /**
     * Returns the element for this package.
     *
     * @return the element for this package
     */
    public PackageElement getElement() {
        return element;
    }

    /** The package name node for the parent package, {@code null} otherwise. */
    public @Nullable PackageNameNode getParent() {
        return parent;
    }

    @Override
    public Tree getTree() {
        return tree;
    }

    @Override
    public  R accept(NodeVisitor visitor, P p) {
        return visitor.visitPackageName(this, p);
    }

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

    @Override
    public boolean equals(@Nullable Object obj) {
        if (!(obj instanceof PackageNameNode)) {
            return false;
        }
        PackageNameNode other = (PackageNameNode) obj;
        return Objects.equals(getParent(), other.getParent())
                && getElement().equals(other.getElement());
    }

    @Override
    public int hashCode() {
        return Objects.hash(getElement(), getParent());
    }

    @Override
    @SideEffectFree
    public Collection getOperands() {
        if (parent == null) {
            return Collections.emptyList();
        }
        return Collections.singleton((Node) parent);
    }
}