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Contracts for Java is a contract programming framework for Java.
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/*
 * Copyright 2010 Google Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 */
package com.google.java.contract;

import java.util.ArrayList;
import java.util.List;

/**
 * Base class for contract assertion errors. You should generally not
 * catch this.
 *
 * @author [email protected] (Nhat Minh Lê)
 */
public abstract class ContractAssertionError extends AssertionError {
  /**
   * Constructs a new ContractAssertionError.
   *
   * @param msg the error message.
   */
  public ContractAssertionError(String msg) {
    super(msg);
    cleanStackTrace();
  }

  /**
   * Constructs a new ContractAssertionError.
   *
   * @param msg the error message.
   * @param throwable the throwable caught while evaluating contracts, or null
   *        for none.
   */
  public ContractAssertionError(String msg, Throwable throwable) {
    this(
        throwable == null
            ? msg
            : "evaluating \"" + msg + "\" caused " + throwable.getClass().getSimpleName());
  }

  /**
   * Constructs a new ContractAssertionError.
   *
   * @param msg the error message.
   * @param cause a previous contract error
   */
  public ContractAssertionError(String msg, ContractAssertionError cause) {
    super(msg);
    initCause(cause);
    cleanStackTrace();
  }

  /**
   * Constructs a new ContractAssertionError.
   *
   * @param msg the error message.
   * @param cause a previous contract error
   * @param throwable the throwable caught while evaluating contracts, or null
   *        for none.
   */
  public ContractAssertionError(String msg, ContractAssertionError cause, Throwable throwable) {
    this(
        throwable == null
            ? msg
            : "evaluating \"" + msg + "\" caused " + throwable.getClass().getSimpleName(),
        cause);
  }

  /**
   * Remove wrapper call, leaving only the contract helper.
   */
  private void cleanStackTrace() {
    StackTraceElement[] realTrace = getStackTrace();
    StackTraceElement[] trace = new StackTraceElement[realTrace.length - 1];
    StackTraceElement top = realTrace[0];
    trace[0] = new StackTraceElement(top.getClassName(),
        getMethodName(realTrace[2].getMethodName()),
        top.getFileName(), top.getLineNumber());
    System.arraycopy(realTrace, 2, trace, 1, realTrace.length - 2);
    setStackTrace(trace);
  }

  public List getMessages() {
    ArrayList list = new ArrayList();
    Throwable error = this;
    do {
      list.add(error.getMessage());
      error = error.getCause();
    } while (error != null);
    return list;
  }

  /**
   * Returns the method name to show in the stack trace instead of the
   * generated method name for the contract.
   */
  protected abstract String getMethodName(String contractedName);
}