Common exceptions in JAVA

Common exceptions in JAVA

1. java. lang. nullpointerexception

This exception is common. The exception is interpreted as "the program encounters a null pointer". Simply put, it calls an uninitialized object or a non-existent object, this error often occurs when you create an image. When you call an array, the image is not initialized, or the path when the image is created is incorrect. There is a null pointer in array operations. In many cases, it is a common mistake for friends who are just learning programming, that is, to confuse array initialization with array element initialization. Array initialization allocates the required space to the array. The elements in the initialized array are not instantiated and are still empty, therefore, you also need to initialize each element (if you want to call it)

 

2. java. lang. classnotfoundexception

This exception is a problem that occurs frequently when many programmers originally developed in development environments such as jb compile the packages under jb in wtk. The exception is interpreted as "the specified class does not exist ", here, we mainly consider whether the class name and path are correct. If the package is made under jb, the package is usually added by default, therefore, add the package path after you go to wtk.

 

3. java. lang. arithmeticexception

This exception is interpreted as "mathematical operation exception". For example, if an operation such as dividing by zero occurs in a program, this exception occurs, we need to check whether the formula is inappropriate in the mathematical operations involved in our program.

 

4. java. lang. arrayindexoutofboundsexception

This exception is often encountered by many friends. The exception is explained as "array subscript out of bounds". Most of the programs now have Array Operations, therefore, when calling an array, you must carefully check whether the subscript you call exceeds the range of the array. In general, it is displayed (that is, the constant is used as the subscript directly) this is not easy to make calls, but implicit (that is, using variables to represent subscript) calls often encounter errors, the length of the array defined in the program is determined by some specific methods, not stated in advance. At this time, it is best to first check the length of the array to avoid this exception.

 

5. java. lang. illegalargumentexception

This exception is interpreted as "parameter errors of methods". Many methods in the j2s' class libraries may cause such errors in some situations, for example, if the volume parameter in the volume adjustment method is written as a negative number, this exception occurs, for example, g. setcolor (int red, int green, int blue) three values in this method, if there is more than 255, this exception will also occur, so once this exception is found, what we need to do, check whether the parameter passing in the method call is incorrect.

 

6. java. lang. illegalaccessexception

This exception is interpreted as "no access permission". This exception occurs when the application calls a class but the current method does not have access permission for this class. Pay attention to this exception when package is used in the program.

 

There are still many other exceptions. I will not list them one by one. What I want to note is that a qualified programmer needs to have a good understanding of common problems in the program and corresponding solutions, otherwise, if you only write the program without modifying the program, it will greatly affect your development. For details about all exceptions, refer to the api.

 

 

 

Arithmetic exception class: ArithmeticExecption

 

Null Pointer exception class: NullPointerException

 

Type forced conversion exception: ClassCastException

 

Array negative subscript exception: NegativeArrayException

 

Array subscript out of bounds exception: ArrayIndexOutOfBoundsException

 

Security violation exception: SecturityException

 

File ended exception: EOFException

 

File not found exception: FileNotFoundException

 

An error occurred while converting the string to a number: NumberFormatException

 

 

Database Operation exception: SQLException

 

 

Input and Output exceptions: IOException

 

 

Method not found exception: NoSuchMethodException

 

Java. lang. AbstractMethodError

 

Incorrect abstract method. Thrown when an application tries to call an abstract method.

 

Java. lang. AssertionError

 

Assertion error. Used to indicate an assertion failure.

 

Java. lang. ClassCircularityError

 

Class loop dependency error. When initializing a class, if the cyclic dependency between classes is detected, this exception is thrown.

 

Java. lang. ClassFormatError

 

Class format error. When the Java Virtual Machine attempts to read a Java class from a file and detects that the content of the file does not conform to the valid format of the class, it throws.

 

Java. lang. Error

 

Error. Is the base class for all errors, used to identify serious program running problems. These problems usually describe abnormal situations that should not be captured by the application.

 

Java. lang. ExceptionInInitializerError

 

Initialization program error. Thrown when an exception occurs during the execution of a class static initialization program. Static initialization programs are static statement segments directly included in the class.

 

Java. lang. IllegalAccessError

 

Illegal access error. This exception is thrown when an application attempts to access, modify the Field of a class, or call its method, but violates the visibility Declaration of the domain or method.

 

Java. lang. IncompatibleClassChangeError

 

Incompatible class change error. This exception is thrown when the class definition on which the method being executed depends is incompatible. This error is easily caused when the Declaration definition of some classes in the application is modified without re-compiling the entire application.

 

Java. lang. InstantiationError

 

Instantiation error. This exception is thrown when an application attempts to construct an abstract class or interface using the new operator of Java.

 

Java. lang. InternalError

 

Internal error. Indicates that an internal error has occurred to the Java VM.

 

Java. lang. LinkageError

 

Link error. This error and all its subclasses indicate that a class depends on other classes. After the class is compiled, the dependent class changes its class definition and does not recompile all the classes, in this case, an error occurs.

 

Java. lang. NoClassDefFoundError

 

Class Definition error not found. This error is thrown when the Java Virtual Machine or classloader tries to instantiate a class but cannot find the definition of the class.

 

Java. lang. NoSuchFieldError

 

Domain does not exist. This error is thrown when an application attempts to access or modify a certain domain without the definition of this domain.

 

Java. lang. NoSuchMethodError

 

The method does not exist. This error is thrown when an application attempts to call a certain method without the definition of this method.

 

Java. lang. OutOfMemoryError

 

Memory insufficiency error. This error is thrown when the available memory is insufficient for the Java Virtual Machine to allocate to an object.

 

Java. lang. StackOverflowError

 

Stack overflow error. This error is thrown when the hierarchy of recursive calls of an application is too deep, resulting in stack overflow.

 

Java. lang. ThreadDeath

 

The thread ends. This error is thrown when the stop method of the Thread class is called to indicate the end of the Thread.

 

Java. lang. UnknownError

 

Unknown error. Used to indicate that the Java Virtual Machine has encountered an unknown serious error.

 

Java. lang. UnsatisfiedLinkError

 

A link error is returned. Thrown when the Java Virtual Machine does not find the native language definition of a class declared as the native method.

 

Java. lang. UnsupportedClassVersionError

 

Unsupported class version error. This error is thrown when the Java Virtual Machine attempts to read a class file but finds that the main and secondary versions of the file are not supported by the current Java virtual machine.

 

Java. lang. VerifyError

 

Verification error. This error is thrown when the validators detect internal incompatibility or security issues in a class file.

 

Java. lang. VirtualMachineError

 

Virtual Machine error. Indicates that the virtual machine is damaged or the resources required to continue the operation are insufficient.

 

 

Java. lang. ArithmeticException

 

Arithmetic condition exception. For example, integer division by zero.

 

Java. lang. ArrayIndexOutOfBoundsException

 

An error occurred while exiting the array index. If the index value of the array is negative or greater than or equal to the size of the array, throw.

 

Java. lang. ArrayStoreException

 

An error occurred while storing the array. It is thrown when a non-array declared object is stored in the array.

 

Java. lang. ClassCastException

 

Class styling exception. Suppose there are classes A and B (A is not the parent class or subclass of B), and O is the instance of A, then this exception is thrown when an instance of Class B is forcibly constructed by O. This exception is often called a forced type conversion exception.

 

Java. lang. ClassNotFoundException

 

Class exception not found. This exception is thrown when the application tries to construct a class based on the class name in the string format and cannot find the class file with the corresponding name after traversing the CLASSPAH.

 

Java. lang. CloneNotSupportedException

 

Clone exceptions are not supported. If the Cloneable interface is not implemented or the clone method is not supported, this exception is thrown when the clone () method is called.

 

Java. lang. EnumConstantNotPresentException

 

The enumerated constant does not exist. This exception is thrown when an application attempts to access an enumeration object by name or enumeration type, but this enumeration object does not contain constants.

 

Java. lang. Exception

 

Root exception. Used to describe what the application wants to capture.

 

Java. lang. IllegalAccessException

 

Illegal access exception. When an application tries to create an instance of a class, access this class attribute, and call this class method through reflection, at that time, the exception could not be thrown when defining the category, attribute, method, or constructor.

 

Java. lang. IllegalMonitorStateException

 

Illegal monitoring status exception. This exception is thrown when a thread tries to wait for a monitor of an object (O) that it does not own or notifies other threads to wait for the monitor of this object (O.

 

Java. lang. IllegalStateException

 

Illegal status exception. If a method is called while the Java environment and application are not in the valid call state of a method, this exception is thrown.

 

Java. lang. IllegalThreadStateException

 

The invalid thread status is abnormal. When the county seat is not in the valid call status of a method and the method is called, an exception is thrown.

 

Java. lang. IndexOutOfBoundsException

 

An exception occurred when the index was out of bounds. This exception is thrown when the index value for accessing a sequence is smaller than 0 or greater than or equal to the sequence size.

 

Java. lang. InstantiationException

 

Instantiation exception. This exception is thrown when an instance of a class is created using the newInstance () method and the class is an abstract class or interface.

 

Java. lang. InterruptedException

 

Aborted exception. This exception is thrown when a Thread is in a long wait, sleep, or other pause State and other threads terminate the Thread through the interrupt method of the Thread.

 

Java. lang. NegativeArraySizeException

 

An error occurred while the array size is negative. This exception is thrown when an array is created with a negative value.

 

Java. lang. NoSuchFieldException

 

The property does not exist. This exception is thrown when you access a non-existent attribute of a class.

 

Java. lang. NoSuchMethodException

 

Method does not have an exception. This exception is thrown when a method that does not exist to access a class.

 

Java. lang. NullPointerException

 

Null Pointer exception. This exception is thrown when the application tries to use null where the object is required. For example, call the instance method of the null object, access the attribute of the null object, calculate the length of the null object, and throw null using the throw statement.

 

Java. lang. NumberFormatException

 

The number format is incorrect. This exception is thrown when you try to convert a String to a specified numeric type that does not meet the numeric type requirements.

 

Java. lang. RuntimeException

 

Exception during running. It is the parent class of all exceptions that can be thrown during normal operations of Java virtual machines.

 

Java. lang. SecurityException

 

Security exception. Thrown by the security manager to indicate exceptions that violate security conditions.

 

Java. lang. StringIndexOutOfBoundsException

 

An exception occurred when the string index was out of bounds. If the index value is used to access a character in a string and the index value is smaller than 0 or greater than or equal to the sequence size, this exception is thrown.

 

Java. lang. TypeNotPresentException

 

Type does not exist. When the application tries

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