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📜  Java中的内置异常及示例

📅  最后修改于: 2022-05-13 01:55:51.943000             🧑  作者: Mango

Java中的内置异常及示例

Java中的异常类型

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中重要的内置异常的列表。
内置异常示例：

  1. 算术异常：在算术运算中发生异常情况时抛出。 
    // 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： 

    Can't divide a number by 0
  2. ArrayIndexOutOfBounds Exception :抛出该异常表示已使用非法索引访问了数组。索引为负数或大于或等于数组的大小。 
    // 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：
     

    Array Index is Out Of Bounds
  3. ClassNotFoundException ：当我们尝试访问未找到定义的类时会引发此异常。 
    // 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： 

    ClassNotFoundException
  4. FileNotFoundException ：当文件不可访问或未打开时引发此异常。 
    // 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： 

    File does not exist
  5. IOException :当输入输出操作失败或中断时抛出
    // 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： 

    error: unreported exception IOException; must be caught or declared to be thrown
  6. InterruptedException ：当线程在等待、休眠或做一些处理时抛出，并被中断。 
    // Java Program to illustrate 
// InterruptedException
class Geeks {
public static void main(String args[])
    {
        Thread t = new Thread();
        t.sleep(10000);
    }
}

    输出： 

    error: unreported exception InterruptedException; must be caught or declared to be thrown
  7. NoSuchMethodException :访问未找到的方法时抛出 t。 
    // 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： 

    error: exception NoSuchMethodException is never thrown 
in body of corresponding try statement
  8. NullPointerException ：引用空对象的成员时会引发此异常。 Null 代表什么都没有
    // 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： 

    NullPointerException..
  9. NumberFormatException ：当方法无法将字符串转换为数字格式时引发此异常。 
    // 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： 

    Number format exception
  10. StringIndexOutOfBoundsException：它由 String 类方法抛出以指示索引为负数而不是字符串的大小。 
    // 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： 

    StringIndexOutOfBoundsException

其他一些重要的例外

  1. ClassCastException 
    // 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： 

    Exception in thread "main" java.lang.ClassCastException: 
java.lang.Object cannot be cast to java.lang.String
  2. 堆栈溢出错误
    // 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： 

    Exception in thread "main" java.lang.StackOverflowError
  3. NoClassDefFoundError 
    // Java Program to illustrate
// NoClassDefFoundError
class Test //
    {
public static void main(String[] args)
    {
        System.out.println("HELLO GEEKS");
    }
}

    输出： 

    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
  4. 异常初始化错误
    代码 1： 
    // Java Program to illustrate 
// ExceptionInInitializerError
class Test {
    static int x = 10 / 0;
public static void main(String[] args)
    {
    }
}

    输出： 

    Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.ArithmeticException: / by zero

    代码 2： 

    // Java Program to illustrate 
// ExceptionInInitializerError
class Test {
    static
    {
        String s = null;
        System.out.println(s.length());
    }
public static void main(String[] args)
    {
    }
}

    输出： 

    Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.NullPointerException

    解释 ：只要在执行静态变量赋值和静态块时发生任何异常，就会发生上述异常。

  5. IllegalArgumentException 
    // 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： 

    Exception in thread "main" java.lang.IllegalArgumentException

    说明：异常由程序员或 API 开发人员显式发生，以指示已使用非法参数调用了方法。

  6. 非法线程状态异常
    // Java Program to illustrate 
// IllegalStateException
class Test {
public static void main(String[] args)
    {
        Thread t = new Thread();
        t.start();
        t.start();
    }
}

    输出： 

    Exception in thread "main" java.lang.IllegalThreadStateException

    解释 ：上述异常由程序员或 API 开发人员显式引发，表明在错误的时间调用了一个方法。

  7. 断言错误
    // 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： 

    Exception in thread "main" java.lang.AssertionError

    解释 ：上述异常由程序员或 API 开发人员显式引发，表明断言语句失败。