AssertionError继承Error，提供了多个构造方法，代码如下：
/*
* 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;
/**
* Thrown when an assertion has failed.
*
* @since 1.4
*/
public class AssertionError extends Error {
private static final long serialVersionUID = -5013299493970297370L;
/**
* Constructs a new {@code AssertionError} with no message.
*/
public AssertionError() {
}
/**
* Constructs a new {@code AssertionError} with the given detail message and cause.
* @since 1.7
* @hide 1.7
*/
public AssertionError(String detailMessage, Throwable cause) {
super(detailMessage, cause);
}
/**
* Constructs a new {@code AssertionError} with a message based on calling
* {@link String#valueOf(Object)} with the specified object. If the object
* is an instance of {@link Throwable}, then it also becomes the cause of
* this error.
*
* @param detailMessage
* the object to be converted into the detail message and
* optionally the cause.
*/
public AssertionError(Object detailMessage) {
super(String.valueOf(detailMessage));
if (detailMessage instanceof Throwable) {
initCause((Throwable) detailMessage);
}
}
/**
* Constructs a new {@code AssertionError} with a message based on calling
* {@link String#valueOf(boolean)} with the specified boolean value.
*
* @param detailMessage
* the value to be converted into the message.
*/
public AssertionError(boolean detailMessage) {
this(String.valueOf(detailMessage));
}
/**
* Constructs a new {@code AssertionError} with a message based on calling
* {@link String#valueOf(char)} with the specified character value.
*
* @param detailMessage
* the value to be converted into the message.
*/
public AssertionError(char detailMessage) {
this(String.valueOf(detailMessage));
}
/**
* Constructs a new {@code AssertionError} with a message based on calling
* {@link String#valueOf(int)} with the specified integer value.
*
* @param detailMessage
* the value to be converted into the message.
*/
public AssertionError(int detailMessage) {
this(Integer.toString(detailMessage));
}
/**
* Constructs a new {@code AssertionError} with a message based on calling
* {@link String#valueOf(long)} with the specified long value.
*
* @param detailMessage
* the value to be converted into the message.
*/
public AssertionError(long detailMessage) {
this(Long.toString(detailMessage));
}
/**
* Constructs a new {@code AssertionError} with a message based on calling
* {@link String#valueOf(float)} with the specified float value.
*
* @param detailMessage
* the value to be converted into the message.
*/
public AssertionError(float detailMessage) {
this(Float.toString(detailMessage));
}
/**
* Constructs a new {@code AssertionError} with a message based on calling
* {@link String#valueOf(double)} with the specified double value.
*
* @param detailMessage
* the value to be converted into the message.
*/
public AssertionError(double detailMessage) {
this(Double.toString(detailMessage));
}
}
其父类Error继承自Throwable，有四个构造方法，如下：
/*
* 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;
/**
* {@code Error} is the superclass of all classes that represent unrecoverable
* errors. When errors are thrown, they should not be caught by application
* code.
*
* @see Throwable
* @see Exception
* @see RuntimeException
*/
public class Error extends Throwable {
private static final long serialVersionUID = 4980196508277280342L;
/**
* Constructs a new {@code Error} that includes the current stack trace.
*/
public Error() {
}
/**
* Constructs a new {@code Error} with the current stack trace and the
* specified detail message.
*
* @param detailMessage
* the detail message for this error.
*/
public Error(String detailMessage) {
super(detailMessage);
}
/**
* Constructs a new {@code Error} with the current stack trace, the
* specified detail message and the specified cause.
*
* @param detailMessage
* the detail message for this error.
* @param throwable
* the cause of this error.
*/
public Error(String detailMessage, Throwable throwable) {
super(detailMessage, throwable);
}
/**
* Constructs a new {@code Error} with the current stack trace and the
* specified cause.
*
* @param throwable
* the cause of this error.
*/
public Error(Throwable throwable) {
super(throwable);
}
}
而Throwable是所有异常和错误的超类，里面有两个native方法，代码如下：
/*
* 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.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import libcore.util.EmptyArray;
/**
* The superclass of all classes which can be thrown by the VM. The
* two direct subclasses are recoverable exceptions ({@code Exception}) and
* unrecoverable errors ({@code Error}). This class provides common methods for
* accessing a string message which provides extra information about the
* circumstances in which the {@code Throwable} was created (basically an error
* message in most cases), and for saving a stack trace (that is, a record of
* the call stack at a particular point in time) which can be printed later.
* <p>
* A {@code Throwable} can also include a cause, which is a nested {@code
* Throwable} that represents the original problem that led to this {@code
* Throwable}. It is often used for wrapping various types of errors into a
* common {@code Throwable} without losing the detailed original error
* information. When printing the stack trace, the trace of the cause is
* included.
*
* @see Error
* @see Exception
* @see RuntimeException
*/
public class Throwable implements java.io.Serializable {
private static final long serialVersionUID = -3042686055658047285L;
/**
* The message provided when the exception was created.
*/
private String detailMessage;
/**
* The cause of this Throwable. Null when there is no cause.
*/
private Throwable cause = this;
/**
* Throwables suppressed by this throwable. Null when suppressed exceptions
* are disabled.
*/
private List<Throwable> suppressedExceptions = Collections.emptyList();
/**
* An intermediate representation of the stack trace. This field may
* be accessed by the VM; do not rename.
*/
private transient volatile Object stackState;
/**
* A fully-expanded representation of the stack trace.
*/
private StackTraceElement[] stackTrace;
/**
* Constructs a new {@code Throwable} that includes the current stack trace.
*/
public Throwable() {
fillInStackTrace();
}
/**
* Constructs a new {@code Throwable} with the current stack trace and the
* specified detail message.
*
* @param detailMessage
* the detail message for this {@code Throwable}.
*/
public Throwable(String detailMessage) {
this();
this.detailMessage = detailMessage;
}
/**
* Constructs a new {@code Throwable} with the current stack trace, the
* specified detail message and the specified cause.
*
* @param detailMessage
* the detail message for this {@code Throwable}.
* @param throwable
* the cause of this {@code Throwable}.
*/
public Throwable(String detailMessage, Throwable throwable) {
this();
this.detailMessage = detailMessage;
cause = throwable;
}
/**
* Constructs a new {@code Throwable} with the current stack trace and the
* specified cause.
*
* @param throwable
* the cause of this {@code Throwable}.
*/
public Throwable(Throwable throwable) {
this();
this.detailMessage = throwable == null ? null : throwable.toString();
cause = throwable;
}
/**
* Constructs a new {@code Throwable} with the current stack trace, the
* specified detail message and the specified cause.
*
* @param enableSuppression if false, throwables passed to {@link
* #addSuppressed(Throwable)} will be silently discarded.
* @since 1.7
* @hide 1.7
*/
protected Throwable(String detailMessage, Throwable throwable, boolean enableSuppression) {
this(detailMessage, throwable);
if (!enableSuppression) {
this.suppressedExceptions = null;
}
}
/**
* Records the stack trace from the point where this method has been called
* to this {@code Throwable}. This method is invoked by the {@code Throwable} constructors.
*
* <p>This method is public so that code (such as an RPC system) which catches
* a {@code Throwable} and then re-throws it can replace the construction-time stack trace
* with a stack trace from the location where the exception was re-thrown, by <i>calling</i>
* {@code fillInStackTrace}.
*
* <p>This method is non-final so that non-Java language implementations can disable VM stack
* traces for their language. Filling in the stack trace is relatively expensive.
* <i>Overriding</i> this method in the root of a language‘s exception hierarchy allows the
* language to avoid paying for something it doesn‘t need.
*
* @return this {@code Throwable} instance.
*/
public Throwable fillInStackTrace() {
// Fill in the intermediate representation
stackState = nativeFillInStackTrace();
// Mark the full representation as empty
stackTrace = null;
return this;
}
/**
* Returns the extra information message which was provided when this
* {@code Throwable} was created. Returns {@code null} if no message was
* provided at creation time.
*
* @return this {@code Throwable}‘s detail message.
*/
public String getMessage() {
return detailMessage;
}
/**
* Returns the extra information message which was provided when this
* {@code Throwable} was created. Returns {@code null} if no message was
* provided at creation time. Subclasses may override this method to return
* localized text for the message. Android returns the regular detail message.
*
* @return this {@code Throwable}‘s localized detail message.
*/
public String getLocalizedMessage() {
return getMessage();
}
/**
* Returns the array of stack trace elements of this {@code Throwable}. Each
* {@code StackTraceElement} represents an entry in the call stack. The
* element at position 0 is the top of the stack, that is, the stack frame
* where this {@code Throwable} is thrown.
*
* @return a copy of the array of {@code StackTraceElement}s representing
* the call stack. Changes in the array obtained from this call will
* not change the call stack stored in this {@code Throwable}.
* @see #printStackTrace()
*/
public StackTraceElement[] getStackTrace() {
return getInternalStackTrace().clone();
}
/**
* Sets the array of stack trace elements. Each {@code StackTraceElement}
* represents an entry in the call stack. A copy of the specified array is
* stored in this {@code Throwable}. will be returned by {@code
* getStackTrace()} and printed by {@code printStackTrace()}.
*
* @param trace
* the new array of {@code StackTraceElement}s. A copy of the
* array is stored in this {@code Throwable}, so subsequent
* changes to {@code trace} will not change the call stack stored
* in this {@code Throwable}.
* @throws NullPointerException
* if any element in {@code trace} is {@code null}.
* @see #printStackTrace()
*/
public void setStackTrace(StackTraceElement[] trace) {
StackTraceElement[] newTrace = trace.clone();
for (int i = 0; i < newTrace.length; i++) {
if (newTrace[i] == null) {
throw new NullPointerException("trace[" + i + "] == null");
}
}
stackTrace = newTrace;
}
/**
* Writes a printable representation of this {@code Throwable}‘s stack trace
* to the {@code System.err} stream.
*
*/
public void printStackTrace() {
printStackTrace(System.err);
}
/**
* Counts the number of duplicate stack frames, starting from the
* end of the stack.
*
* @param currentStack a stack to compare
* @param parentStack a stack to compare
*
* @return the number of duplicate stack frames.
*/
private static int countDuplicates(StackTraceElement[] currentStack,
StackTraceElement[] parentStack) {
int duplicates = 0;
int parentIndex = parentStack.length;
for (int i = currentStack.length; --i >= 0 && --parentIndex >= 0;) {
StackTraceElement parentFrame = parentStack[parentIndex];
if (parentFrame.equals(currentStack[i])) {
duplicates++;
} else {
break;
}
}
return duplicates;
}
/**
* Returns an array of StackTraceElement. Each StackTraceElement
* represents a entry on the stack.
*
* @return an array of StackTraceElement representing the stack
*/
private StackTraceElement[] getInternalStackTrace() {
if (stackTrace == null) {
stackTrace = nativeGetStackTrace(stackState);
stackState = null; // Clean up intermediate representation
}
return stackTrace;
}
/**
* Writes a printable representation of this {@code Throwable}‘s stack trace
* to the specified print stream. If the {@code Throwable} contains a
* {@link #getCause() cause}, the method will be invoked recursively for
* the nested {@code Throwable}.
*
* @param err
* the stream to write the stack trace on.
*/
public void printStackTrace(PrintStream err) {
try {
printStackTrace(err, "", null);
} catch (IOException e) {
// Appendable.append throws IOException but PrintStream.append doesn‘t.
throw new AssertionError();
}
}
/**
* Writes a printable representation of this {@code Throwable}‘s stack trace
* to the specified print writer. If the {@code Throwable} contains a
* {@link #getCause() cause}, the method will be invoked recursively for the
* nested {@code Throwable}.
*
* @param err
* the writer to write the stack trace on.
*/
public void printStackTrace(PrintWriter err) {
try {
printStackTrace(err, "", null);
} catch (IOException e) {
// Appendable.append throws IOException, but PrintWriter.append doesn‘t.
throw new AssertionError();
}
}
/**
* @param indent additional indentation on each line of the stack trace.
* This is the empty string for all but suppressed throwables.
* @param parentStack the parent stack trace to suppress duplicates from, or
* null if this stack trace has no parent.
*/
private void printStackTrace(Appendable err, String indent, StackTraceElement[] parentStack)
throws IOException {
err.append(toString());
err.append("\n");
StackTraceElement[] stack = getInternalStackTrace();
if (stack != null) {
int duplicates = parentStack != null ? countDuplicates(stack, parentStack) : 0;
for (int i = 0; i < stack.length - duplicates; i++) {
err.append(indent);
err.append("\tat ");
err.append(stack[i].toString());
err.append("\n");
}
if (duplicates > 0) {
err.append(indent);
err.append("\t... ");
err.append(Integer.toString(duplicates));
err.append(" more\n");
}
}
// Print suppressed exceptions indented one level deeper.
if (suppressedExceptions != null) {
for (Throwable throwable : suppressedExceptions) {
err.append(indent);
err.append("\tSuppressed: ");
throwable.printStackTrace(err, indent + "\t", stack);
}
}
Throwable cause = getCause();
if (cause != null) {
err.append(indent);
err.append("Caused by: ");
cause.printStackTrace(err, indent, stack);
}
}
@Override
public String toString() {
String msg = getLocalizedMessage();
String name = getClass().getName();
if (msg == null) {
return name;
}
return name + ": " + msg;
}
/**
* Initializes the cause of this {@code Throwable}. The cause can only be
* initialized once.
*
* @param throwable
* the cause of this {@code Throwable}.
* @return this {@code Throwable} instance.
* @throws IllegalArgumentException
* if {@code Throwable} is this object.
* @throws IllegalStateException
* if the cause has already been initialized.
*/
public Throwable initCause(Throwable throwable) {
if (cause != this) {
throw new IllegalStateException("Cause already initialized");
}
if (throwable == this) {
throw new IllegalArgumentException("throwable == this");
}
cause = throwable;
return this;
}
/**
* Returns the cause of this {@code Throwable}, or {@code null} if there is
* no cause.
*
* @return Throwable this {@code Throwable}‘s cause.
*/
public Throwable getCause() {
if (cause == this) {
return null;
}
return cause;
}
/**
* Adds {@code throwable} to the list of throwables suppressed by this. The
* throwable will included when this exception‘s stack trace is printed.
*
* @throws IllegalArgumentException if {@code throwable == this}.
* @throws NullPointerException if {@code throwable == null}.
* @since 1.7
* @hide 1.7
*/
public final void addSuppressed(Throwable throwable) {
if (throwable == this) {
throw new IllegalArgumentException("throwable == this");
}
if (throwable == null) {
throw new NullPointerException("throwable == null");
}
if (suppressedExceptions != null) {
// suppressed exceptions are enabled
if (suppressedExceptions.isEmpty()) {
// ensure we have somewhere to place suppressed exceptions
suppressedExceptions = new ArrayList<Throwable>(1);
}
suppressedExceptions.add(throwable);
}
}
/**
* Returns the throwables suppressed by this.
*
* @since 1.7
* @hide 1.7
*/
public final Throwable[] getSuppressed() {
return (suppressedExceptions != null && !suppressedExceptions.isEmpty())
? suppressedExceptions.toArray(new Throwable[suppressedExceptions.size()])
: EmptyArray.THROWABLE;
}
private void writeObject(ObjectOutputStream out) throws IOException {
// ensure the stackTrace field is initialized
getInternalStackTrace();
out.defaultWriteObject();
}
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
in.defaultReadObject();
if (suppressedExceptions != null) {
// the deserialized list may be unmodifiable, so just create a mutable copy
suppressedExceptions = new ArrayList<Throwable>(suppressedExceptions);
}
}
/*
* Creates a compact, VM-specific collection of goodies, suitable for
* storing in the "stackState" field, based on the current thread‘s
* call stack.
*/
private static native Object nativeFillInStackTrace();
/*
* Creates an array of StackTraceElement objects from the data held
* in "stackState".
*/
private static native StackTraceElement[] nativeGetStackTrace(Object stackState);
}
从源码中容易理解他们的层次和调用关系。
AssertionError、Error和Throwable,布布扣,bubuko.com
AssertionError、Error和Throwable
原文：http://blog.csdn.net/u010142437/article/details/25052509