Java 简明教程

Java - Built-in Exceptions

Built-in Exceptions in Java

exception Java 在标准包 java.lang 中定义了多个类。

Java defines several exception classes inside the standard package java.lang.

这些异常中最通用的异常是标准类型 RuntimeException 的子类。由于 java.lang 隐式导入到了所有 Java 程序中，所以大多数派生自 RuntimeException 的异常都可自动获得。

The most general of these exceptions are subclasses of the standard type RuntimeException. Since java.lang is implicitly imported into all Java programs, most exceptions derived from RuntimeException are automatically available.

Types of Java Built-in Exceptions

Java 中的内置异常分为两类：Checked Exceptions 和 Unchecked Exceptions。

Built-in Exceptions in Java are categorized into two categories Checked Exceptions and Unchecked Exceptions.

Checked Exceptions: The checked exceptions are handled by the programmer during writing the code, they can be handled using the try-catch block. These exceptions are checked at compile-time.
Unchecked Exceptions: The unchecked exceptions are not handled by the programmer. These exceptions are thrown on run-time. Some of the unchecked exceptions are NullPointerException, ArrayIndexOutOfBoundsException, ArithmeticException, etc.

Common Built-in Exceptions in Java

Java 定义了一些其他类型的异常，这些异常与它的各种类库相关。以下是 Java 未经检查和检查的 RuntimeException 的列表。

Java defines several other types of exceptions that relate to its various class libraries. Following is the list of Java Unchecked and Checked RuntimeException.

Sr.No.	Exception & Description
1	ArithmeticException Arithmetic error, such as divide-by-zero.
2	ArrayIndexOutOfBoundsException Array index is out-of-bounds.
3	ArrayStoreException Assignment to an array element of an incompatible type.
4	ClassCastException Invalid cast.
5	IllegalArgumentException Illegal argument used to invoke a method.
6	IllegalMonitorStateException Illegal monitor operation, such as waiting on an unlocked thread.
7	IllegalStateException Environment or application is in incorrect state.
8	IllegalThreadStateException Requested operation not compatible with the current thread state.
9	IndexOutOfBoundsException Some type of index is out-of-bounds.
10	NegativeArraySizeException Array created with a negative size.
11	NullPointerException Invalid use of a null reference.
12	NumberFormatException Invalid conversion of a string to a numeric format.
13	SecurityException Attempt to violate security.
14	StringIndexOutOfBounds Attempt to index outside the bounds of a string.
15	UnsupportedOperationException An unsupported operation was encountered.
16	ClassNotFoundException Class not found.
17	CloneNotSupportedException Attempt to clone an object that does not implement the Cloneable interface.
18	IllegalAccessException Access to a class is denied.
19	InstantiationException Attempt to create an object of an abstract class or interface.
20	InterruptedException One thread has been interrupted by another thread.
21	NoSuchFieldException A requested field does not exist.
22	NoSuchMethodException A requested method does not exist.

Examples of Java Built-in Exception

Example 1: Demonstrating Arithmetic Exception Without try-catch

在此示例中，我们通过将一个值除以 0 来创建错误。在此情况下，未检查异常将被触发。由于未检查，编译器不会报错，并且程序将成功编译。一旦程序运行，异常将被抛出，JVM 将拦截同样的错误并终止程序，而不会打印最后一条语句。

In this example, we’re creating an error by dividing a value by 0. In this case, an unchecked exception will be raised. Being unchecked, compiler won’t complain and program will compile successfully. Once program runs, the exception will be thrown and JVM will intercepts the same and terminate the program before printing the last statement.

package com.tutorialspoint;

public class ExcepTest {

   public static void main(String args[]) {

      int b = 0;
      int c = 1/b;
      System.out.println("c :" + c);
   }
}

Exception in thread "main" java.lang.ArithmeticException: / by zero
	at com.tutorialspoint.ExcepTest.main(ExcepTest.java:8)

Example 2: Demonstrating Arithmetic Exception With try-catch

在此示例中，我们正在处理未检查的异常。第一步，我们通过将一个值除以 0 来生成错误。在此情况下，未检查异常将被触发。我们正在通过 ArithmeticException 来处理。一旦程序运行，异常将被抛出，catch 块会拦截同样的错误，打印最后一条语句。

In this example, we’re handling unchecked exception. As first step, we’re generating an error by dividing a value by 0. In this case, an unchecked exception will be raised. We’re handling via ArithmeticException. Once program runs, the exception will be thrown and catch block will intercepts the same and print the last statement.

package com.tutorialspoint;

public class ExcepTest {

   public static void main(String args[]) {
      try {
         int b = 0;
         int c = 1/b;
         System.out.println("c :" + c);
      }
      catch (ArithmeticException e) {
         System.out.println("Exception thrown  :" + e);
      }
      System.out.println("Out of the block");
   }
}

Exception thrown  :java.lang.ArithmeticException: / by zero
Out of the block

Example 3: Demonstrating No Such Method Exception

在此示例中，我们展示的是：注册异常由否则编译器会抱怨的代码处理。每当方法抛出注册异常时，它都必须处理异常或声明抛出异常语句，正如我们对 getName() 方法所做的那样。当我们尝试运行该方法时，JVM 会抱怨编译问题，如下所示输出中所示：

In this example, we’re showcasing that a checked exception is to be handled by code otherwise compiler will complain. Whenever a method throws a checked exception, it has to either handle the exception or declare throws exception statement as we’re doing for getName() method. When we try to run the method, JVM complains the compilation problem as shown in output listed below:

package com.tutorialspoint;

public class ExcepTest {

   public static void main(String args[]) {
      ExcepTest excepTest = new ExcepTest();
      excepTest.getName();
   }

   private String getName() throws NoSuchMethodException {
	   throw new NoSuchMethodException();
   }
}

Exception in thread "main" java.lang.Error: Unresolved compilation problem:
    Unhandled exception type NoSuchMethodException

    at com.tutorialspoint.ExcepTest.main(ExcepTest.java:7)