我们在定义一个新的异常类时，必须提供这样一个可以包含嵌套异常的构造函数。并有一个私有成员来保存这个“起因异常”。java 代码
public Class ExceptionB extends Exception{
private Throwable cause;
public ExceptionB(String msg, Throwable ex){
super(msg);
this.cause = ex;
}
public ExceptionB(String msg){
super(msg);
}
public ExceptionB(Throwable ex){
this.cause = ex;
}
}
当然，我们在调用printStackTrace方法时，需要把所有的“起因异常”的信息也同时打印出来。所以我们需要覆写printStackTrace方法来显示全部的异常栈跟踪。包括嵌套异常的栈跟踪。java 代码
public void printStackTrace(PrintStrean ps){
if(cause == null){
super.printStackTrace(ps);
}else{
ps.println(this);
cause.printStackTrace(ps);
}
}
一个完整的支持嵌套的checked异常类源码如下。我们在这里暂且把它叫做NestedExceptionjava 代码
public NestedException extends Exception{
private Throwable cause;
public NestedException (String msg){
super(msg);
}
public NestedException(String msg, Throwable ex){
super(msg);
This.cause = ex;
}
public Throwable getCause(){
return (this.cause == null ? this :this.cause);
}
public getMessage(){
String message = super.getMessage();
Throwable cause = getCause();
if(cause != null){
message = message + “;nested Exception is ” + cause;
}
return message;
}
