Java Method类 getParameterCount()用法及代码示例

Method类的java.lang.reflect.Method.getParameterCount()方法返回在方法Object上声明的参数数量。

用法:

public int getParameterCount()

返回值：此方法返回在此方法对象上定义的形式参数的数量。

以下示例程序旨在说明Method类的getParameterCount()方法：

范例1：在下面的程序中，对于作为输入给出的特定方法，返回参数编号。

// Program Demonstrate how to apply getParameterCount() 
// method of Method Class. 
  
import java.lang.reflect.Method; 
  
public class GFG { 
  
    // Main method 
    public static void main(String[] args) 
    { 
  
        try { 
            // create class object 
            Class classobj = GFG.class; 
  
            // get list of methods 
            Method[] methods = classobj.getMethods(); 
  
            // get no of parameters for method setManyValues 
            int noOfParameters = methods[0].getParameterCount(); 
  
            System.out.println("Method Name:"
                               + methods[0].getName()); 
  
            // print no of parameters 
            System.out.println("No of parameters:" + noOfParameters); 
        } 
        catch (Exception e) { 
            e.printStackTrace(); 
        } 
    } 
  
    // method name setManyValues 
    // No of parameters is one for this method 
    public void setManyValues(String parameter1) 
    { 
        System.out.println("setManyValues"); 
    } 
}

输出：

Method Name:setManyValues
No of parameters:1

范例2：在程序下面，返回在类中定义的所有方法的参数编号。

// Program Demonstrate how to apply getParameterCount() method 
// of Method Class. 
  
import java.lang.reflect.Method; 
  
public class GFG { 
  
    // Main method 
    public static void main(String[] args) 
    { 
  
        try { 
            // create class object 
            Class classobj = DemoClass.class; 
  
            // get list of methods 
            Method[] methods = classobj.getMethods(); 
  
            // get no of parameters for each 
            // method in list of methods 
            for (Method method:methods) { 
  
                // print name of method 
                System.out.print("Method Name is "
                                 + method.getName()); 
  
                // get no of parameters for each method 
                int noOfParameters = method.getParameterCount(); 
  
                // print no of parameters 
                System.out.println(" and No of parameters = "
                                   + noOfParameters); 
            } 
        } 
        catch (Exception e) { 
            e.printStackTrace(); 
        } 
    } 
} 
// Demo class to apply getParameterCount() method 
class DemoClass { 
  
    // method name DemoMethod1 
    // No of parameters is 1 for this method 
    public void DemoMethod1(String parameter1) 
    { 
        System.out.println("DemoMethod1"); 
    } 
  
    // method name DemoMethod2 
    // No of parameters is 2 for this method 
    public void DemoMethod2(String parameter1, 
                            String parameter2) 
    { 
        System.out.println("DemoMethod2"); 
    } 
  
    // method name DemoMethod2 
    // No of parameters is Zero for this method 
    public void DemoMethod3() 
    { 
        System.out.println("DemoMethod3"); 
    } 
}

输出：

Method Name is DemoMethod1 and No of parameters = 1
Method Name is DemoMethod2 and No of parameters = 2
Method Name is DemoMethod3 and No of parameters = 0
Method Name is wait and No of parameters = 2
Method Name is wait and No of parameters = 1
Method Name is wait and No of parameters = 0
Method Name is equals and No of parameters = 1
Method Name is toString and No of parameters = 0
Method Name is hashCode and No of parameters = 0
Method Name is getClass and No of parameters = 0
Method Name is notify and No of parameters = 0
Method Name is notifyAll and No of parameters = 0

说明：该程序的输出还显示除类对象中定义的方法(例如，wait，equals，toString，hashCode，getClass，notify，notifyAll)以外的方法对象的结果。这些方法通过类对象从java.lang lang包的超类名称Object继承。

参考： https://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Method.html#getParameterCount-

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注：本文由纯净天空筛选整理自AmanSingh2210大神的英文原创作品 Method Class | getParameterCount() method in Java。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。