Java Method類 getTypeParameters()用法及代碼示例

Method類的java.lang.reflect.Method.getTypeParameters()方法按聲明順序返回此Method對象的泛型聲明所聲明的TypeVariable對象的數組。數組的元素表示由Method聲明的類型變量對象。如果Method Object泛型聲明不包含類型變量，則此getTypeParameters()返回長度為0的數組。

用法:

public TypeVariable<Method>[] getTypeParameters()

返回值：此方法返回此Method對象的通用聲明所聲明的TypeVariable對象的數組

異常：如果此Method對象的通用簽名與JVM規範中指定的格式不匹配，則此方法返回GenericSignatureFormatError。

以下示例程序旨在說明Method類的getTypeParameters()方法：

範例1：

說明：此代碼獲取一個類的所有Method的列表。然後，如果在聲明這些方法時定義了一些TypeVariable，則通過循環對其進行迭代，並獲取TypeVariable。如果這些方法有一些TypeVariable可用，則將打印TypeVariable名稱。

/* 
* Program Demonstrate getTypeParameters() method  
* of Method Class. 
*/
import java.lang.reflect.Method; 
import java.lang.reflect.TypeVariable; 
  
public class GFG { 
  
    // In this method, there is a 
    // Type parameter N which extends Number class 
    public <N extends Number> void getSampleMethod(N n) 
    { 
    } 
  
    // create main method 
    public static void main(String args[]) 
    { 
  
        try { 
  
            // create class object for class name GFG 
            Class c = GFG.class; 
  
            // get list of all Method objects of class GFG 
            Method[] methods = c.getMethods(); 
  
            // loop through all methods and 
            // try to get Type Parameter of Method 
            for (Method m:methods) { 
  
                // get TypeVariable array by getTypeParameters() method 
                TypeVariable[] types = m.getTypeParameters(); 
  
                // print Type Parameter details for every TypeVariable 
                for (TypeVariable t:types) { 
  
                    // print type parameter name 
                    // along with there method name 
                    System.out.println("Type variable for Method Name "
                                       + m.getName() + " is "
                                       + t.getName()); 
                } 
            } 
        } 
        catch (Exception e) { 
  
            // print Exception Messgae if 
            // any exception occured in program 
            e.printStackTrace(); 
        } 
    } 
}

輸出：

Type variable for Method Name getSampleMethod is N

範例2：在此程序中，有多個類型的方法參數。在此程序中，使用getTypeParameter()函數獲取類型參數，並打印這些類型參數的詳細信息。

/* 
* Program Demonstrate getTypeParameters() method  
* of Method Class having more than one type  
parameter of methods 
*/
import java.lang.*; 
  
public class GFG { 
  
    // In this method, 
    // there are three Type parameters 
    // N which extends Number class, 
    // E extends RuntimeException Class 
    // and C extends Character class. 
    public <N extends Number, 
                      E extends RuntimeException, 
                                C extends Character> void
    getSampleMethod(N n) throws E 
    { 
    } 
  
    // In this method, 
    // there are Two Type parameters:
    // A which extends the ArrayList class, 
    // L extends the LinkedList class 
    public <A extends ArrayList, L extends LinkedList> L 
    SetSampleMethod(A a, L l) 
    { 
        return l; 
    } 
  
    // create main method of class 
    public static void main(String args[]) 
    { 
  
        try { 
  
            // create class object for 
            // class name GFG to get methods list 
            // of GFG class 
            Class c = GFG.class; 
  
            // get list of all Method objects of 
            // class GFG in array of Methods 
            Method[] methods = c.getMethods(); 
  
            // loop through all methods and 
            // try to get Type Parameter of Method 
            for (Method m:methods) { 
  
                // get TypeVariable array by 
                // getTypeParameters method 
                TypeVariable[] types = m.getTypeParameters(); 
  
                // If there are 1 or more than 1 
                // type variables for the current 
                // method of loop then print method name 
                if (types.length > 0) 
                    System.out.println("\nType variable Details"
                                       + " for Method Name "
                                       + m.getName()); 
  
                // print Type Parameter details 
                // for Current Method of loop 
                for (TypeVariable t:types) { 
                    // get bounds for current TypeVariable 
                    // and print the Name of TypeVariable and bounds 
                    Type[] bounds = t.getBounds(); 
  
                    // print TypeVariable name and Bounds 
                    System.out.println("Name:"
                                       + t.getName()); 
                    System.out.println("Bounds:"
                                       + Arrays.toString(bounds)); 
                } 
            } 
        } 
        catch (Exception e) { 
            // print Exception message if some Exception occurs 
            e.printStackTrace(); 
        } 
    } 
}

輸出：

Type variable Details for Method Name getSampleMethod
Name:N
Bounds:[class java.lang.Number]
Name:E
Bounds:[class java.lang.RuntimeException]
Name:C
Bounds:[class java.lang.Character]

Type variable Details for Method Name SetSampleMethod
Name:A
Bounds:[class java.util.ArrayList]
Name:L
Bounds:[class java.util.LinkedList]

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

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注：本文由純淨天空篩選整理自AmanSingh2210大神的英文原創作品 Method Class | getTypeParameters() Method in Java。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。