What are the common exceptions in java

1. NullPointerException:

Null pointer exception, this exception will be thrown when operating the method or property of a null object. It is a very troublesome exception, because it is a runtime exception and does not need to be caught manually, but encountering this exception during runtime will interrupt the program. (Recommended learning: java course)

2. OutOfMemoryError:

Memory overflow exception, which is not controllable by the program. The memory of the object that needs to be allocated exceeds the current maximum heap memory. You need to adjust the heap memory size (-Xmx) and optimize the program.

3. IOException:

IO, that is: Input, Output, which often occurs when we read and write disk files and network content. Exception, this exception is a checked exception and needs to be caught manually.

For example, reading and writing files requires throwing an exception:

public int read() throws IOException
public void write(int b) throws IOException

4. FileNotFoundException:

Cannot find file exception , this exception will be thrown if the file does not exist.

If you define an input and output file stream, an error will be reported if the file does not exist:

public FileInputStream(File file) throws FileNotFoundException
public FileOutputStream(File file) throws FileNotFoundException

FileNotFoundException is actually a subclass of IOException. It is also a checked exception and needs to be caught manually.

5. ClassNotFoundException:

The class cannot be found exception. This is an exception often encountered in Java development. This is thrown when loading a class. That is, the specified class cannot be loaded on the classpath. It is a checked exception and needs to be caught manually.

public static <T> Class<T> getExistingClass(ClassLoader classLoader, String className) {
  try {
     return (Class<T>) Class.forName(className, true, classLoader);
  }
  catch (ClassNotFoundException e) {
     return null;
  }
}

6. ClassCastException:

Class conversion exception. This exception will be thrown when converting an instance that is not this class into this class.

If you force a number into a string, this exception will be reported:

Object x = new Integer(0);
System.out.println((String)x);

It is a runtime exception and does not need to be caught manually.

The above is the detailed content of What are the common exceptions in java. For more information, please follow other related articles on the PHP Chinese website!