Java Reflection - Method.getTypeParameters() Examples

Class:

java.lang.reflect.Method

Method:

public TypeVariable<Method>[] getTypeParameters()

Returns an array of TypeVariable objects that represent the type variables declared by this method.

Examples

package com.logicbig.example.method;

import javax.swing.*;
import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.util.Arrays;

public class GetTypeParametersExample {

    private static <N extends Number, C extends JComponent> void process(N n, C c) {}

    public static void main(String... args) throws NoSuchMethodException {
        Method m = GetTypeParametersExample.class.getDeclaredMethod("process", Number.class,
                JComponent.class);
        TypeVariable<Method>[] typeParameters = m.getTypeParameters();
        System.out.println(Arrays.toString(typeParameters));
        for (TypeVariable<Method> typeParameter : typeParameters) {
            printTypeVariable(typeParameter, 1);
        }
    }

    private static void printTypeVariable(TypeVariable type, int level) {
        print(level, "TypeVariable#getName(): " + type.getName());
        Type[] bounds = type.getBounds();
        print(level, "TypeVariable#getBounds(): " + Arrays.toString(bounds));
        for (Type bound : bounds) {
            print(level, "TypeVariable#bound: " + bound);
            printType(bound, level + 1);
        }
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            return;
        }
        if (type instanceof Class) {
            print(level, "type is an instance of Class");
            print(level, "Class Name: " + ((Class) type).getName());
        } else {
            throw new RuntimeException("not expected");
        }
    }

    private static void print(int level, String string) {
        System.out.printf("%" + (level * 4 - 3) + "s\u00A6- %s%n", "", string);
    }
}

Output

[N, C]
 ¦- TypeVariable#getName(): N
 ¦- TypeVariable#getBounds(): [class java.lang.Number]
 ¦- TypeVariable#bound: class java.lang.Number
     ¦- type is an instance of Class
     ¦- Class Name: java.lang.Number
 ¦- TypeVariable#getName(): C
 ¦- TypeVariable#getBounds(): [class javax.swing.JComponent]
 ¦- TypeVariable#bound: class javax.swing.JComponent
     ¦- type is an instance of Class
     ¦- Class Name: javax.swing.JComponent

package com.logicbig.example.method;

import javax.swing.*;
import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.util.Arrays;
import java.util.Objects;

public class GetTypeParametersExample2 {

    private static <N extends Number, C extends JComponent> void process() {}

    public static void main(String... args) throws NoSuchMethodException {
        Method m = GetTypeParametersExample2.class.getDeclaredMethod("process");
        TypeVariable<Method>[] typeParameters = m.getTypeParameters();
        System.out.println(Arrays.toString(typeParameters));
        for (TypeVariable<Method> typeParameter : typeParameters) {
            printTypeVariable(typeParameter, 1);
        }
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            return;
        }
        print(level, "type: " + Objects.toString(type));
        if (type instanceof TypeVariable) {
            print(level, "type is an instance of TypeVariable");
            printTypeVariable((TypeVariable) type, level + 1);
        } else if (type instanceof Class) {
            print(level, "type is an instance of Class");
            print(level, "Class Name: " + ((Class) type).getName());
        } else {
            throw new RuntimeException();
        }
    }

    private static void printTypeVariable(TypeVariable type, int level) {
        print(level, "TypeVariable#getName(): " + type.getName());
        Type[] bounds = type.getBounds();
        print(level, "TypeVariable#getBounds(): " + Arrays.toString(bounds));
        for (Type bound : bounds) {
            print(level, "TypeVariable#bound: " + bound);
            printType(bound, level + 1);
        }
    }

    private static void print(int level, String string) {
        System.out.printf("%" + (level * 4 - 3) + "s\u00A6- %s%n", "", string);
    }
}

Output

[N, C]
 ¦- TypeVariable#getName(): N
 ¦- TypeVariable#getBounds(): [class java.lang.Number]
 ¦- TypeVariable#bound: class java.lang.Number
     ¦- type: class java.lang.Number
     ¦- type is an instance of Class
     ¦- Class Name: java.lang.Number
 ¦- TypeVariable#getName(): C
 ¦- TypeVariable#getBounds(): [class javax.swing.JComponent]
 ¦- TypeVariable#bound: class javax.swing.JComponent
     ¦- type: class javax.swing.JComponent
     ¦- type is an instance of Class
     ¦- Class Name: javax.swing.JComponent

package com.logicbig.example.method;

import javax.swing.*;
import java.lang.reflect.Method;
import java.lang.reflect.TypeVariable;
import java.util.Arrays;

public class GetTypeParametersExample3<N extends Number, C extends JComponent> {

    //this method does not declare any type variable
    private void process(N n, C c) {
    }

    public static void main(String... args) throws NoSuchMethodException {
        Method m = GetTypeParametersExample3.class.getDeclaredMethod("process", Number.class, JComponent.class);
        TypeVariable<Method>[] typeParameters = m.getTypeParameters();
        System.out.println(Arrays.toString(typeParameters));
    }
}

Output

[]

package com.logicbig.example.method;

import java.lang.reflect.Method;
import java.lang.reflect.TypeVariable;
import java.util.*;

public class GetTypeParametersExample4 {

    public static void main(String... args) {
        for (Method method : ArrayList.class.getDeclaredMethods()) {
            TypeVariable<Method>[] tps = method.getTypeParameters();
            if (tps.length > 0) {
                System.out.printf("method: %s, typeVariables: %s%n", method, Arrays.toString(tps));
            }
        }
    }
}

Output

method: public java.lang.Object[] java.util.ArrayList.toArray(java.lang.Object[]), typeVariables: [T]
method: static java.lang.Object java.util.ArrayList.elementAt(java.lang.Object[],int), typeVariables: [E]

Java Reflection - Method.getTypeParameters() Examples

Class:

Method:

Examples

Output

Output

Output

Output

See Also