Java 中的 Class getDeclaredConstructor()方法，带示例
原文:https://www . geesforgeks . org/class-getdeclaredconstructor-method-in-Java-with-examples/
java.lang.Class 类 的 getDeclaredConstructor() 方法用于获取该类的具有指定参数类型的指定构造函数。方法以 constructor 对象的形式返回此类的指定构造函数。
语法:
public Constructor<T>
getDeclaredConstructor(Class[] parameterType)
throws NoSuchMethodException, SecurityException
参数:该构造函数接受一个参数 parameterType ，它是指定构造函数的参数类型数组。
返回值:该方法以 constructor 对象的形式返回该类的指定构造函数。
异常此方法抛出:
- 如果找不到指定名称的构造函数，则 NoSuchMethodException 。
-
SecurityException if a security manager is present and the security conditions are not met.
下面的程序演示了 getDeclaredConstructor()方法。
例 1:
```java // Java program to demonstrate // getDeclaredConstructor() method
import java.util.*;
public class Test {
public Test() {}
public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {
// returns the Class object for this class Class myClass = Class.forName("Test");
System.out.println("Class represented by myClass: " + myClass.toString());
Class[] parameterType = null;
// Get the constructor of myClass // using getDeclaredConstructor() method System.out.println( "Constructor of myClass: " + myClass.getDeclaredConstructor(parameterType)); } } ```
Output:
```java Class represented by myClass: class Test Constructor of myClass: public Test()
```
例 2:
```java // Java program to demonstrate // getDeclaredConstructor() constructor
import java.util.*;
class Main {
private Main() {}
public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {
// returns the Class object for this class Class myClass = Class.forName("Main");
System.out.println("Class represented by myClass: " + myClass.toString());
Class[] parameterType = new Class[1]; parameterType[0] = Long.class;
try { // Get the constructor of myClass // using getDeclaredConstructor() method System.out.println( "Constructor of myClass: " + myClass.getDeclaredConstructor(parameterType)); } catch (Exception e) { System.out.println(e); } } } ```
Output:
java Class represented by myClass: class Main java.lang.NoSuchMethodException: Main.(java.lang.Long)
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