C_C 的和Java的异常机制

文章作者 100test 发表时间 2007:03:14 16:37:57
来源 100Test.Com百考试题网

程序总会出现异常的，需要我们去处理。C＋＋和JAVA都有自己异常机制，我们应该遵循着去处理异常。那它们的异常机制有何异同呢？

要注意一点：异常机制处理异常是要付出代价的，即异常处理的代码比无异常处理的要慢好多倍。

JAVA的异常机制

在面向对象的世界里，一切都是对象，JAVA的异常也不例外。API中异常类的“始祖”是 Throwable 类，有 Exception 类和 Error 类直接继承Throwable 。Error是很严重的，是不可挽救的，我们一般是通过继承Throwable 或Exception 来定义自己的异常类。

先看看API（这里是从1.5摘抄的）里的两个异常类是怎样的？

import java.io.*.
public class Throwable implements Serializable ...{
/** *//** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = -3042686055658047285L.

/** *//**
* Native code saves some indication of the stack backtrace in this slot.
*/
private transient Object backtrace.
private String detailMessage.
private Throwable cause = this.
private StackTraceElement[] stackTrace.

public Throwable() ...{
fillInStackTrace().
}

public Throwable(String message) ...{
fillInStackTrace().
detailMessage = message.
}

public Throwable(String message, Throwable cause) ...{
fillInStackTrace().
detailMessage = message.
this.cause = cause.
}

public String getLocalizedMessage() ...{
return getMessage().
}

public Throwable getCause() ...{
return (cause==this ? null : cause).
}

public synchronized Throwable initCause(Throwable cause) ...{
if (this.cause != this)
throw new IllegalStateException("Cant overwrite cause").
if (cause == this)
throw new IllegalArgumentException("Self-causation not permitted").
this.cause = cause.
return this.
}

public String toString() ...{
String s = getClass().getName().
String message = getLocalizedMessage().
return (message != null) ? (s ": " message) : s.
}

private synchronized StackTraceElement[] getOurStackTrace() ...{
// Initialize stack trace if this is the first call to this method
if (stackTrace == null) ...{
int depth = getStackTraceDepth().
stackTrace = new StackTraceElement[depth].
for (int i=0. i < depth. i )
stackTrace[i] = getStackTraceElement(i).
}
return stackTrace.
}
//......省略了一些
}

注意一点：异常类是可串行化的。来源：www.examda.com 　

public class Exception extends Throwable {
static final long serialVersionUID = -3387516993124229948L.

public Exception() {
super().
}

public Exception(String message) {
super(message).
}

public Exception(String message, Throwable cause) {
super(message, cause).
}

public Exception(Throwable cause) {
super(cause).
}
}