Java - 自定义异常

Java 自定义异常

自定义异常指的是根据需要创建您自己的异常来定制异常。自定义异常派生自Exception类。

Java 自定义异常的必要性

• 根据项目中不同类型的错误对异常进行分类。
• 允许应用程序级别的异常处理。

在 Java 中创建自定义异常

要创建自定义异常，需要创建一个类，该类必须继承自 Exception 类。

语法

以下是 Java 中创建自定义类的语法：

class MyException extends Exception {
}

您只需要扩展预定义的Exception类即可创建您自己的异常。这些被认为是已检查异常。

创建自定义异常的规则

编写您自己的异常类时，请记住以下几点：

• 所有异常都必须是 Throwable 的子类。

• 如果要编写由“处理或声明”规则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，则需要扩展 RuntimeException 类。

Java 自定义异常示例

下面的InsufficientFundsException类是一个用户定义的异常，它扩展了 Exception 类，使其成为一个已检查异常。异常类就像任何其他类一样，包含有用的字段和方法。

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

为了演示使用我们用户定义的异常，下面的 CheckingAccount 类包含一个抛出 InsufficientFundsException 的 withdraw() 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.tutorialspoint;

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.tutorialspoint.InsufficientFundsException
	at com.tutorialspoint.CheckingAccount.withdraw(BankDemo.java:39)
	at com.tutorialspoint.BankDemo.main(BankDemo.java:14)

在下一个示例中，我们将自定义异常声明为 RuntimeException，使其成为未检查异常类，如下所示：

class MyException extends RuntimeException {
}

通过扩展 RuntimeException 创建自定义类的示例

我们扩展预定义的RuntimeException类来创建您自己的异常作为未检查异常。下面的InsufficientFundsException类是一个用户定义的异常，它扩展了 RuntimeException 类，使其成为未检查异常。RuntimeException 类就像任何其他类一样，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;
   }
}

下面的 BankDemo 程序演示了使用未检查异常调用 CheckingAccount 的 deposit() 和 withdraw() 方法。

package com.tutorialspoint;

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.tutorialspoint.InsufficientFundsException
	at com.tutorialspoint.CheckingAccount.withdraw(BankDemo.java:35)
	at com.tutorialspoint.BankDemo.main(BankDemo.java:13)