/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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 General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.lang;

import java.util.Objects;

/**

 * An element in a stack trace, as returned by {@link

 * Throwable#getStackTrace()}.  Each element represents a single stack frame.

 * All stack frames except for the one at the top of the stack represent

 * a method invocation.  The frame at the top of the stack represents the

 * execution point at which the stack trace was generated.  Typically,

 * this is the point at which the throwable corresponding to the stack trace

 * was created.

 *

 * @since  1.4

 * @author Josh Bloch

 */

public final class StackTraceElement implements java.io.Serializable {

    // Normally initialized by VM (public constructor added in 1.5)

    private String declaringClass;

    private String methodName;

    private String fileName;

    private int    lineNumber;

    /**

     * Creates a stack trace element representing the specified execution

     * point.

     *

     * @param declaringClass the fully qualified name of the class containing

     *        the execution point represented by the stack trace element

     * @param methodName the name of the method containing the execution point

     *        represented by the stack trace element

     * @param fileName the name of the file containing the execution point

     *         represented by the stack trace element, or {@code null} if

     *         this information is unavailable

     * @param lineNumber the line number of the source line containing the

     *         execution point represented by this stack trace element, or

     *         a negative number if this information is unavailable. A value

     *         of -2 indicates that the method containing the execution point

     *         is a native method

     * @throws NullPointerException if {@code declaringClass} or

     *         {@code methodName} is null

     * @since 1.5

     */

    public StackTraceElement(String declaringClass, String methodName,

                             String fileName, int lineNumber) {

        this.declaringClass = Objects.requireNonNull(declaringClass, "Declaring class is null");

        this.methodName     = Objects.requireNonNull(methodName, "Method name is null");

        this.fileName       = fileName;

        this.lineNumber     = lineNumber;

    }

    /**

     * Returns the name of the source file containing the execution point

     * represented by this stack trace element.  Generally, this corresponds

     * to the {@code SourceFile} attribute of the relevant {@code class}

     * file (as per <i>The Java Virtual Machine Specification</i>, Section

     * 4.7.7).  In some systems, the name may refer to some source code unit

     * other than a file, such as an entry in source repository.

     *

     * @return the name of the file containing the execution point

     *         represented by this stack trace element, or {@code null} if

     *         this information is unavailable.

     */

    public String getFileName() {

        return fileName;

    }

    /**

     * Returns the line number of the source line containing the execution

     * point represented by this stack trace element.  Generally, this is

     * derived from the {@code LineNumberTable} attribute of the relevant

     * {@code class} file (as per <i>The Java Virtual Machine

     * Specification</i>, Section 4.7.8).

     *

     * @return the line number of the source line containing the execution

     *         point represented by this stack trace element, or a negative

     *         number if this information is unavailable.

     */

    public int getLineNumber() {

        return lineNumber;

    }

    /**

     * Returns the fully qualified name of the class containing the

     * execution point represented by this stack trace element.

     *

     * @return the fully qualified name of the {@code Class} containing

     *         the execution point represented by this stack trace element.

     */

    public String getClassName() {

        return declaringClass;

    }

    /**

     * Returns the name of the method containing the execution point

     * represented by this stack trace element.  If the execution point is

     * contained in an instance or class initializer, this method will return

     * the appropriate <i>special method name</i>, {@code <init>} or

     * {@code <clinit>}, as per Section 3.9 of <i>The Java Virtual

     * Machine Specification</i>.

     *

     * @return the name of the method containing the execution point

     *         represented by this stack trace element.

     */

    public String getMethodName() {

        return methodName;

    }

    /**

     * Returns true if the method containing the execution point

     * represented by this stack trace element is a native method.

     *

     * @return {@code true} if the method containing the execution point

     *         represented by this stack trace element is a native method.

     */

    public boolean isNativeMethod() {

        return lineNumber == -2;

    }

    /**

     * Returns a string representation of this stack trace element.  The

     * format of this string depends on the implementation, but the following

     * examples may be regarded as typical:

     * <ul>

     * <li>

     *   {@code "MyClass.mash(MyClass.java:9)"} - Here, {@code "MyClass"}

     *   is the <i>fully-qualified name</i> of the class containing the

     *   execution point represented by this stack trace element,

     *   {@code "mash"} is the name of the method containing the execution

     *   point, {@code "MyClass.java"} is the source file containing the

     *   execution point, and {@code "9"} is the line number of the source

     *   line containing the execution point.

     * <li>

     *   {@code "MyClass.mash(MyClass.java)"} - As above, but the line

     *   number is unavailable.

     * <li>

     *   {@code "MyClass.mash(Unknown Source)"} - As above, but neither

     *   the file name nor the line  number are available.

     * <li>

     *   {@code "MyClass.mash(Native Method)"} - As above, but neither

     *   the file name nor the line  number are available, and the method

     *   containing the execution point is known to be a native method.

     * </ul>

     * @see    Throwable#printStackTrace()

     */

    public String toString() {

        return getClassName() + "." + methodName +

            (isNativeMethod() ? "(Native Method)" :

             (fileName != null && lineNumber >= 0 ?

              "(" + fileName + ":" + lineNumber + ")" :

              (fileName != null ?  "("+fileName+")" : "(Unknown Source)")));

    }

    /**

     * Returns true if the specified object is another

     * {@code StackTraceElement} instance representing the same execution

     * point as this instance.  Two stack trace elements {@code a} and

     * {@code b} are equal if and only if:

     * <pre>

     *     equals(a.getFileName(), b.getFileName()) &&

     *     a.getLineNumber() == b.getLineNumber()) &&

     *     equals(a.getClassName(), b.getClassName()) &&

     *     equals(a.getMethodName(), b.getMethodName())

     * </pre>

     * where {@code equals} has the semantics of {@link

     * java.util.Objects#equals(Object, Object) Objects.equals}.

     *

     * @param  obj the object to be compared with this stack trace element.

     * @return true if the specified object is another

     *         {@code StackTraceElement} instance representing the same

     *         execution point as this instance.

     */

    public boolean equals(Object obj) {

        if (obj==this)

            return true;

        if (!(obj instanceof StackTraceElement))

            return false;

        StackTraceElement e = (StackTraceElement)obj;

        return e.declaringClass.equals(declaringClass) &&

            e.lineNumber == lineNumber &&

            Objects.equals(methodName, e.methodName) &&

            Objects.equals(fileName, e.fileName);

    }

    /**

     * Returns a hash code value for this stack trace element.

     */

    public int hashCode() {

        int result = 31*declaringClass.hashCode() + methodName.hashCode();

        result = 31*result + Objects.hashCode(fileName);

        result = 31*result + lineNumber;

        return result;

    }

    private static final long serialVersionUID = 6992337162326171013L;

}