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Java example source code file (StackTraceElement.java)

This example Java source code file (StackTraceElement.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

declaring, method, native, source, stacktraceelement, string, unknown, util

The StackTraceElement.java Java example source code

/*
 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 * 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, 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, {@code } or
     * {@code <clinit>}, as per Section 3.9 of 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 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>{@code
     *     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;
}

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