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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 java.util.Collection;
import java.util.Collections;
import java.util.Objects;
import javax.lang.model.element.VariableElement;
import org.checkerframework.checker.nullness.qual.Nullable;
import org.checkerframework.javacutil.ElementUtils;
import org.checkerframework.javacutil.TreeUtils;

/**
 * A node for a field access, including a method accesses:
 *
 *  *   expression . field
 * 
 */
public class FieldAccessNode extends Node {

  protected final Tree tree;
  protected final VariableElement element;
  protected final String field;
  protected final Node receiver;

  // TODO: add method to get modifiers (static, access level, ..)

  /**
   * Creates a new FieldAccessNode.
   *
   * @param tree the tree from which to create a FieldAccessNode
   * @param receiver the receiver for the resuling FieldAccessNode
   */
  public FieldAccessNode(Tree tree, Node receiver) {
    super(TreeUtils.typeOf(tree));
    assert TreeUtils.isFieldAccess(tree);
    this.tree = tree;
    this.receiver = receiver;
    this.field = TreeUtils.getFieldName(tree);

    if (tree instanceof MemberSelectTree) {
      MemberSelectTree mstree = (MemberSelectTree) tree;
      assert TreeUtils.isUseOfElement(mstree) : "@AssumeAssertion(nullness): tree kind";
      this.element = (VariableElement) TreeUtils.elementFromUse(mstree);
    } else {
      assert tree instanceof IdentifierTree;
      IdentifierTree itree = (IdentifierTree) tree;
      assert TreeUtils.isUseOfElement(itree) : "@AssumeAssertion(nullness): tree kind";
      this.element = (VariableElement) TreeUtils.elementFromUse(itree);
    }
  }

  public FieldAccessNode(Tree tree, VariableElement element, Node receiver) {
    super(element.asType());
    this.tree = tree;
    this.element = element;
    this.receiver = receiver;
    this.field = element.getSimpleName().toString();
  }

  public VariableElement getElement() {
    return element;
  }

  public Node getReceiver() {
    return receiver;
  }

  public String getFieldName() {
    return field;
  }

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

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

  @Override
  public String toString() {
    return getReceiver() + "." + field;
  }

  /** Is this a static field? */
  public boolean isStatic() {
    return ElementUtils.isStatic(getElement());
  }

  @Override
  public boolean equals(@Nullable Object obj) {
    if (!(obj instanceof FieldAccessNode)) {
      return false;
    }
    FieldAccessNode other = (FieldAccessNode) obj;
    return getReceiver().equals(other.getReceiver()) && getFieldName().equals(other.getFieldName());
  }

  @Override
  public int hashCode() {
    return Objects.hash(getReceiver(), getFieldName());
  }

  @Override
  public Collection getOperands() {
    return Collections.singletonList(receiver);
  }
}