C / C++的和Java的异常机制[1]

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() ...{

字串6

return getMessage();
}

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

public synchronized Throwable initCause(Throwable cause) ...{
if (this.cause != this)
throw new IllegalStateException("Can’t 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;
} 字串7

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 stackTrace[i] = getStackTraceElement(i);
}
return stackTrace;
}
　//......省略了一些
　}

　　注意一点：异常类是可串行化的。

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

public Exception() {
super();

字串1

}

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

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

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