Java 内置异常，示例
原文:https://www . geesforgeks . org/build-exceptions-Java-examples/
内置异常是 Java 库中可用的异常。这些异常适用于解释某些错误情况。下面是 Java 中重要的内置异常列表。 内置异常示例:
-
Arithmetic exception : It is thrown when an exceptional condition has occurred in an arithmetic operation.
java // Java program to demonstrate // ArithmeticException class ArithmeticException_Demo { public static void main(String args[]) { try { int a = 30, b = 0; int c = a / b; // cannot divide by zero System.out.println("Result = " + c); } catch (ArithmeticException e) { System.out.println("Can't divide a number by 0"); } } }输出:
```java Can't divide a number by 0
```
-
ArrayIndexOutOfBounds Exception : It is thrown to indicate that an array has been accessed with an illegal index. The index is either negative or greater than or equal to the size of the array.
java // Java program to demonstrate // ArrayIndexOutOfBoundException class ArrayIndexOutOfBound_Demo { public static void main(String args[]) { try { int a[] = new int[5]; a[6] = 9; // accessing 7th element in an array of // size 5 } catch (ArrayIndexOutOfBoundsException e) { System.out.println("Array Index is Out Of Bounds"); } } }输出:
java Array Index is Out Of Bounds -
ClassNotFoundException : This Exception is raised when we try to access a class whose definition is not found.
```java // Java program to illustrate the // concept of ClassNotFoundException class Bishal {
} class Geeks {
} class MyClass { public static void main(String[] args) { Object o = class.forName(args[0]).newInstance(); System.out.println("Class created for" + o.getClass().getName()); } } ```
输出:
java ClassNotFoundException -
FileNotFoundException : This Exception is raised when a file is not accessible or does not open.
```java // Java program to demonstrate // FileNotFoundException import java.io.File; import java.io.FileNotFoundException; import java.io.FileReader; class File_notFound_Demo {
public static void main(String args[]) { try {
// Following file does not exist File file = new File("E:// file.txt");
FileReader fr = new FileReader(file); } catch (FileNotFoundException e) { System.out.println("File does not exist"); } } } ```
输出:
java File does not exist -
IOException : It is thrown when an input-output operation failed or interrupted
java // Java program to illustrate IOException import java.io.*; class Geeks { public static void main(String args[]) { FileInputStream f = null; f = new FileInputStream("abc.txt"); int i; while ((i = f.read()) != -1) { System.out.print((char)i); } f.close(); } }输出:
```java error: unreported exception IOException; must be caught or declared to be thrown
```
-
InterruptedException : It is thrown when a thread is waiting, sleeping, or doing some processing, and it is interrupted.
java // Java Program to illustrate // InterruptedException class Geeks { public static void main(String args[]) { Thread t = new Thread(); t.sleep(10000); } }输出:
```java error: unreported exception InterruptedException; must be caught or declared to be thrown
```
-
NoSuchMethodException : t is thrown when accessing a method which is not found.
```java // Java Program to illustrate // NoSuchMethodException class Geeks { public Geeks() { Class i; try { i = Class.forName("java.lang.String"); try { Class[] p = new Class[5]; } catch (SecurityException e) { e.printStackTrace(); } catch (NoSuchMethodException e) { e.printStackTrace(); } } catch (ClassNotFoundException e) { e.printStackTrace(); } }
public static void main(String[] args) { new Geeks(); } } ```
输出:
```java error: exception NoSuchMethodException is never thrown in body of corresponding try statement
```
-
NullPointerException : This exception is raised when referring to the members of a null object. Null represents nothing
java // Java program to demonstrate NullPointerException class NullPointer_Demo { public static void main(String args[]) { try { String a = null; // null value System.out.println(a.charAt(0)); } catch (NullPointerException e) { System.out.println("NullPointerException.."); } } }输出:
```java NullPointerException..
```
-
NumberFormatException : This exception is raised when a method could not convert a string into a numeric format.
```java // Java program to demonstrate // NumberFormatException class NumberFormat_Demo { public static void main(String args[]) { try { // "akki" is not a number int num = Integer.parseInt("akki");
System.out.println(num); } catch (NumberFormatException e) { System.out.println("Number format exception"); } } } ```
输出:
```java Number format exception
```
-
StringIndexOutOfBoundsException : It is thrown by String class methods to indicate that an index is either negative than the size of the string.
java // Java program to demonstrate // StringIndexOutOfBoundsException class StringIndexOutOfBound_Demo { public static void main(String args[]) { try { String a = "This is like chipping "; // length is 22 char c = a.charAt(24); // accessing 25th element System.out.println(c); } catch (StringIndexOutOfBoundsException e) { System.out.println("StringIndexOutOfBoundsException"); } } }输出:
```java StringIndexOutOfBoundsException
```
其他一些重要的例外情况
-
ClassCastException
java // Java Program to illustrate // ClassCastException class Test { public static void main(String[] args) { String s = new String("Geeks"); Object o = (Object)s; Object o1 = new Object(); String s1 = (String)o1; } }输出:
```java Exception in thread "main" java.lang.ClassCastException: java.lang.Object cannot be cast to java.lang.String
```
-
StackOverflowError
java // Java Program to illustrate // StackOverflowError class Test { public static void main(String[] args) { m1(); } public static void m1() { m2(); } public static void m2() { m1(); } }输出:
```java Exception in thread "main" java.lang.StackOverflowError
```
-
NoClassDefFoundError
java // Java Program to illustrate // NoClassDefFoundError class Test // { public static void main(String[] args) { System.out.println("HELLO GEEKS"); } }输出:
```java Note: If the corresponding Test.class file is not found during compilation then we will get Run-time Exception saying Exception in thread "main" java.lang.NoClassDefFoundError
```
-
ExceptionInInitializerError Code 1:
java // Java Program to illustrate // ExceptionInInitializerError class Test { static int x = 10 / 0; public static void main(String[] args) { } }输出:
```java Exception in thread "main" java.lang.ExceptionInInitializerError Caused by: java.lang.ArithmeticException: / by zero
```
代码 2 :
java // Java Program to illustrate // ExceptionInInitializerError class Test { static { String s = null; System.out.println(s.length()); } public static void main(String[] args) { } }输出:
```java Exception in thread "main" java.lang.ExceptionInInitializerError Caused by: java.lang.NullPointerException
```
说明:每当执行静态变量赋值和静态块时，如果出现异常，就会出现上述异常。
-
IllegalArgumentException
java // Java Program to illustrate // IllegalArgumentException class Test { public static void main(String[] args) { Thread t = new Thread(); Thread t1 = new Thread(); t.setPriority(7); // Correct t1.setPriority(17); // Exception } }输出:
```java Exception in thread "main" java.lang.IllegalArgumentException
```
解释:异常由程序员或应用编程接口开发人员显式发生，以指示某个方法已被非法参数调用。
-
IllegalThreadStateException
java // Java Program to illustrate // IllegalStateException class Test { public static void main(String[] args) { Thread t = new Thread(); t.start(); t.start(); } }输出:
```java Exception in thread "main" java.lang.IllegalThreadStateException
```
解释:以上异常由程序员或 API 开发人员显式上升，表示某个方法在错误的时间被调用。
-
AssertionError
java // Java Program to illustrate // AssertionError class Test { public static void main(String[] args) { // If x is not greater than or equal to 10 // then we will get the run-time exception assert(x >= 10); } }输出:
```java Exception in thread "main" java.lang.AssertionError
```
解释:以上异常由程序员或 API 开发者显式上升，表示 assert 语句失败。
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