Framework: semi-finished software, which can be developed on the basis of framework and simplify coding
Reflection: Encapsulating the components of a class into other objects is the mechanism of reflection
Benefits: * You can manipulate these objects while the program is running. * Can be decoupled, improve the scalability of the program.Copy the code1. Basic Concepts
In reflection, it is also possible to get the complete structure of a class by reflection, using the following classes in the java.lang.Reflect package:
Constructor: indicates the Constructor of a class. Field: indicates the attributes of a class. Method: indicates the methods of a classCopy the codeThese three classes are all subclasses of AccessibleObject:
interface China{
public static final String NATIONAL = "China";
public static final String AUTHOR = "Java";
public void sayChina(a);// Define an abstract method with no parameters
public String sayHello(String name,int age);// Define an abstract method with parameters
}
class Person implements China{
private String name;
private int age;
public Person(a){}public Person(String name){// Declare a constructor for one argument
this.name = name;
}
public Person(String name,int age){
this(name);
this.setAge(age);
}
public String getName(a) {
return name;
}
public void setName(String name) {
this.name = name;
}
public void setAge(int age) {
this.age = age;
}
@Override
public void sayChina(a) {
System.out.println("Author:" + AUTHOR + Nationality: + NATIONAL);
}
@Override
public String sayHello(String name, int age) {
return name + "Hello! I this year" + age + "Age!; }}Copy the codeTwo, to achieve all the interface
To obtain all interfaces implemented by a Class, we must use the getInterfaces() method of the Class Class, which defines:
public Class[] getInterfaces()
Copy the codeThe getInterfaces() method returns an array of objects of the Class, which is then output directly using the getName() method of the Class.
public class Root{
public static void main(String[] args) { Class<? > c1 =null;// Declare the Class object
try{
c1 = Class.forName("Person");
}catch(ClassNotFoundException e){ e.printStackTrace(); } Class<? > c[] = c1.getInterfaces();// Get all the interfaces implemented
for (int i=0; i<c.length; i++){ System.out.println("Implemented interface name:" + c[i].getName());// Output interface name}}}Copy the codeBecause an interface is a special form of a Class, and a Class can implement multiple interfaces, all interface objects are returned in the form of a Class array, and the contents are output in a loop
Get the parent class
A Class can implement multiple interfaces, but can only inherit one parent Class. To get a parent Class, use the getSuperclass() method of the Class Class. This method defines:
public Class<? super T> getSuperclass()
Copy the codeThe getSuperclass() method returns an instance of the Class, and as with the previous interface, you can get the name from the getName() method.
public class Test{
public static void main(String[] args) { Class<? > c1 =null;
try {
c1 = Class.forName("Person");
}catch(ClassNotFoundException e){ e.printStackTrace(); } Class<? > c2 = c1.getSuperclass();// Get the parent information
System.out.println("Parent name:"+ c2.getName()); }}Copy the code
Fourthly, obtain all construction methods
To get all constructors in a Class, you must use the getConstructors() method of the Class Class.
- Gets all the constructors of the Person class
import java.lang.reflect.Constructor;
public class Test{
public static void main(String[] args) { Class<? > c1 =null;
try {
c1 = Class.forName("Person");
}catch(ClassNotFoundException e){ e.printStackTrace(); } Constructor<? > con[] = c1.getConstructors();// Get all the constructors
for (int i=0; i<con.length; i++){ System.out.println("Construction method:"+ con[i]); }}}Copy the code- Gets all the constructors of a class
import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;
public class Test{
public static void main(String[] args) { Class<? > c1 =null;
try {
c1 = Class.forName("Person");
}catch(ClassNotFoundException e){ e.printStackTrace(); } Constructor<? > con[] = c1.getConstructors();// Get all the constructors
for (int i=0; i<con.length; i++){ Class<? > p[] = con[i].getParameterTypes();// Lists the parameter types in the construct
System.out.print("Construction method:");
int mo = con[i].getModifiers();// Access permission
System.out.print(Modifier.toString(mo) + "");// Restore permissions
System.out.print(con[i].getName());// Prints the constructor name
System.out.print("(");
for (int j=0; j<p.length; j++){ System.out.print(p[j].getName() +" arg" + i);
if (j<p.length-1) {// Print the parameter type to determine whether to print ","
System.out.print(",");
}
}
System.out.println("{}"); }}}Copy the code
Five, get all the methods
To get all the methods in a Class, use the Class ClassgetMethods()Method, which returns an array of objects of the Method class. Common methods of this method:
Get all method definitions of a class:
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
public class Test{
public static void main(String[] args) { Class<? > c1 =null;
try {
c1 = Class.forName("Person");
}catch (ClassNotFoundException e){
e.printStackTrace();
}
Method m[] = c1.getMethods();// Get all the methods
for (int i=0; i<m.length; i++){ Class<? > r = m[i].getReturnType();// Retrieve the return value type of the methodClass<? > p[] = m[i].getParameterTypes();// Get all the argument types
int xx = m[i].getModifiers();// Get the modifier for the method
System.out.print(Modifier.toString(xx) + "");// Restore the modifier
System.out.print(r.getName() + "");// Get the method name
System.out.print(m[i].getName());// Get the method name
System.out.print("(");
for (int x=0; x<p.length; x++){ System.out.print(p[x].getName() +"" + "arg" + x);// Output parameters
if (x<p.length-1){
System.out.print(",");// determine whether to print ","} } Class<? > ex[] = m[i].getExceptionTypes();// Get all exceptions thrown
if (ex.length>0){
System.out.print(") throws ");// Outputs ") throws"
}else {
System.out.print(")");
}
for (int j=0; j<ex.length; j++){ System.out.print(ex[j].getName());// Output abnormal information
if (j<ex.length-1){
System.out.print(","); } } System.out.println(); }}}Copy the codeDevelopment tools take advantage of reflection
Get all attributes
It is also possible to obtain all attributes of a class in a reflection operation. There are two different operations:
Get a public property in the implemented interface or superclass:public Field[] getFields() throwsSecurityException gets all the attributes in this class:public Field[] getDeclareDeclaredFields() throws SecurityException
Copy the codeThe above methods return an array of fields. Each Field object represents an attribute in the class. To obtain further information about the attribute, use:
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
public class Test{
public static void main(String[] args) { Class<? > c1 =null;
try {
c1 = Class.forName("Person");
}catch (ClassNotFoundException e){
e.printStackTrace();
}
{// Plain code block
Field f[] = c1.getDeclaredFields();// Get this class attribute
for (int i=0; i<f.length; i++){ Class<? > r = f[i].getType();// Get the type of the attribute
int mo = f[i].getModifiers();// Get the modifier number
String priv = Modifier.toString(mo);// Get the modifier for the property
System.out.print("Attributes of this class:");
System.out.print(priv + "");// Output modifiers
System.out.print(r.getName() + "");// Output attribute type
System.out.print(f[i].getName());// Output the attribute name
System.out.println(";");/ / a newline
}
}
System.out.println("= = = = = = = = = = = = = = = = = = = = = = = = = = =");
{
Field f[] = c1.getFields();// Get the parent public attribute
for (int i=0; i<f.length; i++){ Class<? > r = f[i].getType();// Get the type of the attribute
int mo = f[i].getModifiers();// Get the modifier number
String priv = Modifier.toString(mo);// Get the property modifier
System.out.print("Public property:");
System.out.print(priv + "");// Output modifiers
System.out.print(r.getName() + "");// Output parameter type
System.out.print(f[i].getName());// Output the attribute name
System.out.println(";"); }}}}Copy the code