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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package java.lang;

import java.io.Serializable;

/**
 * A representation of a single stack frame. Arrays of {@code StackTraceElement}
 * are stored in {@link Throwable} objects to represent the whole state of the
 * call stack at the time a {@code Throwable} gets thrown.
 *
 * @see Throwable#getStackTrace()
 */
public final class StackTraceElement implements Serializable {

    private static final long serialVersionUID = 6992337162326171013L;

    private static final int NATIVE_LINE_NUMBER = -2;

    String declaringClass;

    String methodName;

    String fileName;

    int lineNumber;

    /**
     * Constructs a new {@code StackTraceElement} for a specified execution
     * point.
     *
     * @param cls
     *            the fully qualified name of the class where execution is at.
     * @param method
     *            the name of the method where execution is at.
     * @param file
     *            The name of the file where execution is at or {@code null}.
     * @param line
     *            the line of the file where execution is at, a negative number
     *            if unknown or {@code -2} if the execution is in a native
     *            method.
     * @throws NullPointerException
     *             if {@code cls} or {@code method} is {@code null}.
     */
    public StackTraceElement(String cls, String method, String file, int line) {
        if (cls == null) {
            throw new NullPointerException("cls == null");
        } else if (method == null) {
            throw new NullPointerException("method == null");
        }
        declaringClass = cls;
        methodName = method;
        fileName = file;
        lineNumber = line;
    }

    /**
     * Private constructor used by BugVM only.
     */
    @SuppressWarnings("unused")
    private StackTraceElement(Class cls, String method, String file, int line) {
        this(cls.getName(), method, file, line);
    }
    
    /**
     * Compares this instance with the specified object and indicates if they
     * are equal. In order to be equal, the following conditions must be
     * fulfilled:
     * 
    *
  • {@code obj} must be a stack trace element,
  • *
  • the method names of this stack trace element and of {@code obj} must * not be {@code null},
  • *
  • the class, method and file names as well as the line number of this * stack trace element and of {@code obj} must be equal.
  • *
* * @param obj * the object to compare this instance with. * @return {@code true} if the specified object is equal to this * {@code StackTraceElement}; {@code false} otherwise. * @see #hashCode */ @Override public boolean equals(Object obj) { if (!(obj instanceof StackTraceElement)) { return false; } StackTraceElement castObj = (StackTraceElement) obj; /* * Unknown methods are never equal to anything (not strictly to spec, * but spec does not allow null method/class names) */ if ((methodName == null) || (castObj.methodName == null)) { return false; } if (!getMethodName().equals(castObj.getMethodName())) { return false; } if (!getClassName().equals(castObj.getClassName())) { return false; } String localFileName = getFileName(); if (localFileName == null) { if (castObj.getFileName() != null) { return false; } } else { if (!localFileName.equals(castObj.getFileName())) { return false; } } if (getLineNumber() != castObj.getLineNumber()) { return false; } return true; } /** * Returns the fully qualified name of the class belonging to this * {@code StackTraceElement}. * * @return the fully qualified type name of the class */ public String getClassName() { return (declaringClass == null) ? "" : declaringClass; } /** * Returns the name of the Java source file containing class belonging to * this {@code StackTraceElement}. * * @return the name of the file, or {@code null} if this information is not * available. */ public String getFileName() { return fileName; } /** * Returns the line number in the source for the class belonging to this * {@code StackTraceElement}. * * @return the line number, or a negative number if this information is not * available. */ public int getLineNumber() { return lineNumber; } /** * Returns the name of the method belonging to this {@code * StackTraceElement}. * * @return the name of the method, or "" if this information * is not available. */ public String getMethodName() { return (methodName == null) ? "" : methodName; } @Override public int hashCode() { /* * Either both methodName and declaringClass are null, or neither are * null. */ if (methodName == null) { // all unknown methods hash the same return 0; } // declaringClass never null if methodName is non-null return methodName.hashCode() ^ declaringClass.hashCode(); } /** * Indicates if the method name returned by {@link #getMethodName()} is * implemented as a native method. * * @return {@code true} if the method in which this stack trace element is * executing is a native method; {@code false} otherwise. */ public boolean isNativeMethod() { return lineNumber == NATIVE_LINE_NUMBER; } @Override public String toString() { StringBuilder buf = new StringBuilder(80); buf.append(getClassName()); buf.append('.'); buf.append(getMethodName()); if (isNativeMethod()) { buf.append("(Native Method)"); } else { String fName = getFileName(); if (fName == null) { buf.append("(Unknown Source)"); } else { int lineNum = getLineNumber(); buf.append('('); buf.append(fName); if (lineNum >= 0) { buf.append(':'); buf.append(lineNum); } buf.append(')'); } } return buf.toString(); } }




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