Classification of general anomalies
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Java has a very powerful exception handling mechanism. The ancestor of the exception is Throwable, which has the following two subclasses:
Error: indicates an error. After the error occurs, the programmer cannot correct it by means of code, and can only be avoided in advance, just like life has stopped.
Exception: indicates an exception. After the exception occurs, the programmer can correct it by means of code to make the program continue to run, which must be dealt with
Exceptions are divided into compile-time exceptions and runtime exceptions .
Compile-time exceptions are also called compile-time monitored exceptions: during program compilation, non-runtime exceptions are detected, and the exceptions are either thrown upwards or caught.
Runtime exceptions (runtimeException and its subclasses): Runtime exceptions are detected during program compilation, and exceptions can be thrown directly on or inside the function, without capture and declaration.
Classification of general anomalies
How to handle exceptions
Throw an exception throw
Declare exception throws up
Exception catch try-catch to handle it yourself
static String[] usernames={"张三","赵四","王五"};
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
System.out.println("请输入注册的名字！");
String next = sc.next();
//try-catch捕获异常
try {
checkUsername(next);
} catch (RegisterException e) {
e.printStackTrace();
}
}
public static void checkUsername(String usrename) throws RegisterException {//声明异常
for (String name : usernames) {
if (name.equals(usrename)){
throw new RegisterException("亲，该用户已经被注册！");//抛出异常
}
}
System.out.println("恭喜您，注册成功！");
}How to print exceptions
public String getMessage (): Get the description information of the exception and the reason (when prompted to the user, the reason of the error will be prompted.
public String toString (): Get the type and description of the exception (not used).
public void printStackTrace (): Print the abnormal trace stack information and output to the console
Exception with inheritance
If the parent class throws multiple exceptions, when the child class overrides the parent class method, it will throw the same exception as the parent class or a subclass of the parent class exception or not throw an exception.
The method of the parent class does not throw an exception, and the subclass cannot throw an exception when it overrides the method of the parent class. At this time, the subclass generates the exception and can only be caught and processed, and cannot be declared to be thrown
Custom exception class
Need to inherit Exception (compiler exception) or RunTimeException (runtime exception)
public class RegisterException extends Exception {
public RegisterException() {
}
public RegisterException(String message){
super(message);
}
}