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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.block;

import java.util.List;
import java.util.Set;
import org.checkerframework.checker.nullness.qual.Nullable;
import org.checkerframework.dataflow.cfg.node.Node;
import org.checkerframework.dataflow.qual.Pure;
import org.plumelib.util.UniqueId;

/** Represents a basic block in a control flow graph. */
public interface Block extends UniqueId {

  /** The types of basic blocks. */
  public static enum BlockType {

    /** A regular basic block. */
    REGULAR_BLOCK,

    /** A conditional basic block. */
    CONDITIONAL_BLOCK,

    /** A special basic block. */
    SPECIAL_BLOCK,

    /** A basic block that can throw an exception. */
    EXCEPTION_BLOCK,
  }

  /**
   * Returns the type of this basic block.
   *
   * @return the type of this basic block
   */
  BlockType getType();

  /**
   * Returns the predecessors of this basic block.
   *
   * @return the predecessors of this basic block
   */
  Set getPredecessors();

  /**
   * Returns the successors of this basic block.
   *
   * @return the successors of this basic block
   */
  Set getSuccessors();

  /**
   * Returns the nodes contained within this basic block. The list may be empty.
   *
   * The following invariant holds.
   *
   * 
   * forall n in getNodes() :: n.getBlock() == this
   * 
   *
   * @return the nodes contained within this basic block
   */
  @Pure
  List getNodes();

  /**
   * Returns the last node of this block, or null if none.
   *
   * @return the last node of this block or {@code null}
   */
  @Nullable Node getLastNode();
}