On class in Java

Class is the implementation of a specific class defined in the Java language. The definition of a class includes member variables, member methods, the interface implemented by the class, and the parent class of the class. The class object is used to represent the classes and interfaces in the currently running Java application. For example, each array belongs to a class object, and all arrays with the same element type and dimension share a class object. Basic Java types (Boolean, byte, char, short, int, long, float and double) and void types can also be represented as class objects.

The following example uses a class object to display the class name of an object:

We all know that all Java classes inherit from the object class. There is a method in the object class: getclass() This method is used to obtain the class reference of the instantiated object of the class. This reference points to the class object (ha ha, a little awkward). We can't generate a class object ourselves (the constructor is private), and the class object is automatically created by the Java virtual machine when the class is called in, Or generated by the defineclass method in the class loader. The objects we generate will have a field to record the location of the class to which the object belongs in the object of class class. As shown in the figure below:

We can treat each class object as a proxy for many classes. In addition, there will be a field in each class object to record the class loader of the class it refers to. If this field is null, it means that the loader of this class is bootstrap loader For specific reasons, see the article "working mechanism of classloader" I shared before.

We know that there are multiple loaders in Java, and each loader can load multiple classes, so as long as you get the class object, you can use its getclassloader () method to get the reference of the class loader.

The JVM is a unique class object for each kind of manager. Therefore, we can compare objects with the double equal sign operator: A1 getClass()==A.class; Should return true.

Forname (string classname) and forname (string classname, {*} Boolean initialize, * classloader * Loader) * methods.

This method returns the class object corresponding to the given string name. Given the full pathname of a class or interface, this method attempts to locate, load, and connect the class. If successful, this type of object is returned. Otherwise, a classnotfoundexception exception is thrown. For example, the following code snippet returns the name Java Run class descriptor for lang. thread. Classt=Class. forName("java.lang.Thread"); This method needs to specify the class loader. When the forname method with only one string parameter is used, the class object will call the current class loader as the loader by default and set the second parameter to true. The second parameter description: if false, the forname method is called only to load the class in the command class loader without initializing the static block of the class. The static block is called only when the class is instantiated for the first time. When true, the static block is called at load time.

getClassLoader()

Gets the class loader for the class.

getComponentType()

If the current class represents an array, the class object representing the array component is returned; otherwise, null is returned.

getConstructor(Class[])

Returns the specified public constructor sub object of the class represented by the current class object.

getConstructors()

Returns an array of all public constructor sub objects of the class represented by the current class object.

getDeclaredConstructor(Class[])

Returns a specified construction sub object of the class represented by the current class object.

getDeclaredConstructors()

Returns an array of all described construction sub objects of the class represented by the current class object.

getDeclaredField(String)

Returns a specified domain object of the class or interface represented by the current class object.

getDeclaredFields()

Returns an array of all described domain objects of the class or interface represented by the current class object.

getDeclaredMethod(String,Class[])

Returns a specified method object of the class or interface represented by the current class object.

getDeclaredMethods()

Returns an array of all the described methods of the class or interface represented by the class object.

getField(String)

Returns the specified public member domain object of the class or interface represented by the current class object.

getFields()

Returns an array of all accessible public domain objects of the class or interface represented by the current class object.

getInterfaces()

Returns the interface implemented by the class or interface represented by the current object.

getmethod(String,Class[])

Returns the specified public member method object of the class or interface represented by the current class object.

getmethods()

Returns an array of all public member method objects of the class or interface represented by the current class object, including declared and inherited methods from the parent class.

getModifiers()

Returns the Java language modifier code for the class or interface.

getName()

Returns the full pathname string of the type (class, interface, array, or base type) represented by the class object.

getResource(String)

Finds a resource by the specified name.

getResourceAsStream(String)

Find a resource with a given name.

getSigners()

Gets the class tag.

getSuperclass()

If this object represents any class other than object, the parent object of this object is returned.

isArray()

If the class object represents an array, it returns true; otherwise, it returns false.

isAssignableFrom(Class)

Determines whether the class or interface represented by the class object is the same as the class or interface represented by the class specified by the parameter, or is its parent class.

isinstance(Object)

This method is a dynamic equivalent method of instanceof operation in Java language.

isInterface()

Determines whether the specified class object represents an interface type.

isPrimitive()

Determines whether the specified class object represents a Java base type.

newInstance()

Create a new instance of the class.

toString()

Converts an object to a string.

summary

The above is all about talking about class classes in Java. I hope it will be helpful to you. Interested friends can continue to refer to other related topics on this site. If there are deficiencies, please leave a message to point out. Thank you for your support!