什么时候应该用Java创建用户定义的异常类？
我们应该在Java中创建自己的异常。在编写我们自己的异常类时，请记住以下几点
所有异常都必须是Throwable的子级。
如果我们要编写一个由Handle或DelareRule自动执行的检查异常，则需要扩展Exception类。
如果要编写运行时异常，则需要扩展RuntimeException类。
我们可以如下定义自己的Exception类：
class MyException extends Exception {
}我们只需要扩展Exception类来创建我们自己的Exception类。这些被视为检查异常。以下InsufficientFundsException类是用户定义的异常，它扩展了Exception类，使其成为受检查的异常。
示例
// File Name InsufficientFundsException.java
import java.io.*;
class InsufficientFundsException extends Exception {
private double amount;
public InsufficientFundsException(double amount) {
this.amount = amount;
}
public double getAmount() {
return amount;
}
}
//文件名CheckingAccount.java-
class CheckingAccount {
private double balance;
private int number;
public CheckingAccount(int number) {
this.number = number;
}
public void deposit(double amount) {
balance += amount;
}
public void withdraw(double amount) throws InsufficientFundsException {
if(amount <= balance) {
balance -= amount;
}
else {
double needs = amount - balance;
throw new InsufficientFundsException(needs);
}
}
public double getBalance() {
return balance;
}
public int getNumber() {
return number;
}
}
//文件名BankDemo.java-
public class BankDemo {
public static void main(String [] args) {
CheckingAccount c = new CheckingAccount(101);
System.out.println("Depositing $500...");
c.deposit(500.00);
try {
System.out.println("\nWithdrawing $100...");
c.withdraw(100.00);
System.out.println("\nWithdrawing $600...");
c.withdraw(600.00);
} catch(InsufficientFundsException e) {
System.out.println("Sorry, but you are short $" + e.getAmount());
e.printStackTrace();
}
}
}输出结果
Depositing $500... Withdrawing $100... Withdrawing $600... Sorry, but you are short $200.0 InsufficientFundsException at CheckingAccount.withdraw(BankDemo.java:32) at BankDemo.main(BankDemo.java:53)