您可以在 Java 中创建自己的异常。在编写自己的异常类时，请记住以下几点 -

  • 所有异常必须是 Throwable 的子级。

  • 如果要编写由 Handle 或 Declare Rule 自动强制执行的已检查异常，则需要扩展 Exception 类。

  • 如果要编写运行时异常，您需要扩展 RuntimeException 类。

我们可以定义自己的 Exception 类，如下所示 -

class MyException extends Exception {
}

您只需扩展预定义的 Exception 类来创建您自己的异常。这些被认为是检查异常。下面的 InsufficientFundsException 类是一个用户定义的异常，它扩展了 Exception 类，使其成为受检查的异常。异常类与任何其他类一样，包含有用的字段和方法。

示例 1

class InsufficientFundsException extends Exception {
   private double amount;
   
   public InsufficientFundsException(double amount) {
      this.amount = amount;
   }
   
   public double getAmount() {
      return amount;
   }
}

为了演示如何使用我们的用户定义异常，以下 CheckingAccount 类包含withdraw()抛出 InsufficientFundsException 的方法。

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;
   }
}

下面的 BankDemo 程序演示了调用 CheckingAccount 的 Deposit() 和 Withdraw() 方法。

package com.yxjc123;

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();
      }
   }
}

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;
   }
}

class InsufficientFundsException extends Exception {
   private double amount;
   
   public InsufficientFundsException(double amount) {
      this.amount = amount;
   }
   
   public double getAmount() {
      return amount;
   }
}

输出

编译全部以上三个文件并运行BankDemo。这将产生以下结果 -

Depositing $500...

Withdrawing $100...

Withdrawing $600...
Sorry, but you are short $200.0
com.yxjc123.InsufficientFundsException
	at com.yxjc123.CheckingAccount.withdraw(BankDemo.java:39)
	at com.yxjc123.BankDemo.main(BankDemo.java:14)

在下一个示例中，我们将自定义异常声明为 RuntimeException，使其成为未经检查的异常类，如下 -

class MyException extends RuntimeException {
}

示例 2

我们正在扩展预定义的 RuntimeException 类来创建您自己的异常作为未经检查的异常。下面的 InsufficientFundsException 类是一个用户定义的异常，它扩展了 RuntimeException 类，使其成为未经检查的异常。 RuntimeException 类与任何其他类一样，包含有用的字段和方法。

class InsufficientFundsException extends RuntimeException {
   private double amount;
   
   public InsufficientFundsException(double amount) {
      this.amount = amount;
   }
   
   public double getAmount() {
      return amount;
   }
}

以下 BankDemo 程序演示了如何使用未经检查的异常调用 CheckingAccount 的 Deposit() 和 Pulling() 方法。

package com.yxjc123;

public class BankDemo {

   public static void main(String [] args) {
      CheckingAccount c = new CheckingAccount(101);
      System.out.println("Depositing $500...");
      c.deposit(500.00);
      
      System.out.println("\nWithdrawing $100...");
      c.withdraw(100.00);
      System.out.println("\nWithdrawing $600...");
      c.withdraw(600.00);

   }
}

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) {
      if(amount <= balance) {
         balance -= amount;
      }else {
         double needs = amount - balance;
         throw new InsufficientFundsException(needs);
      }
   }
   
   public double getBalance() {
      return balance;
   }
   
   public int getNumber() {
      return number;
   }
}

class InsufficientFundsException extends RuntimeException {
   private double amount;
   
   public InsufficientFundsException(double amount) {
      this.amount = amount;
   }
   
   public double getAmount() {
      return amount;
   }
}

输出

编译并运行BankDemo。这将产生以下结果 -

Depositing $500...

Withdrawing $100...

Withdrawing $600...
Exception in thread "main" 
com.yxjc123.InsufficientFundsException
	at com.yxjc123.CheckingAccount.withdraw(BankDemo.java:35)
	at com.yxjc123.BankDemo.main(BankDemo.java:13)