Java反射方法之getDeclaredMethods和getMethods方法

話不多說先上demo和結果

package com.huawei.test.base;

import java.util.Arrays;

/**
 * @description:
 * @author 無極之嵐
 * @date 2022/2/26 2:20 PM
 */
class MethodTest {

    class Father{
        private void m1(){
            System.out.println("father私有方法");
        }
        public void m2(){
            System.out.println("father公有方法");
        }
    }
    class Son extends Father{
        private void m3(){
            System.out.println("son私有方法");
        }

        public void m4(){
            System.out.println("son公有方法");
        }
    }


    public static void main(String[] args) {
        System.out.println("getDeclaredMethods:");
        Arrays.stream(Son.class.getDeclaredMethods()).forEach(m-> System.out.println(m.getName()));

        System.out.println("getMethods:");
        Arrays.stream(Son.class.getMethods()).forEach(m-> System.out.println(m.getName()));
    }
}

從運行結果可知getDeclaredMethods方法獲取本類的所有方法而getMethods獲取本類及其父類的所有public方法。

翻一下源碼的解釋

/**
     *
     * Returns an array containing {@code Method} objects reflecting all the
     * declared methods of the class or interface represented by this {@code
     * Class} object, including public, protected, default (package)
     * access, and private methods, but excluding inherited methods.
     *
     * <p> If this {@code Class} object represents a type that has multiple
     * declared methods with the same name and parameter types, but different
     * return types, then the returned array has a {@code Method} object for
     * each such method.
     *
     * <p> If this {@code Class} object represents a type that has a class
     * initialization method {@code <clinit>}, then the returned array does
     * <em>not</em> have a corresponding {@code Method} object.
     *
     * <p> If this {@code Class} object represents a class or interface with no
     * declared methods, then the returned array has length 0.
     *
     * <p> If this {@code Class} object represents an array type, a primitive
     * type, or void, then the returned array has length 0.
     *
     * <p> The elements in the returned array are not sorted and are not in any
     * particular order.
     *
     * @return  the array of {@code Method} objects representing all the
     *          declared methods of this class
     * @throws  SecurityException
     *          If a security manager, <i>s</i>, is present and any of the
     *          following conditions is met:
     *
     *          <ul>
     *
     *          <li> the caller's class loader is not the same as the
     *          class loader of this class and invocation of
     *          {@link SecurityManager#checkPermission
     *          s.checkPermission} method with
     *          {@code RuntimePermission("accessDeclaredMembers")}
     *          denies access to the declared methods within this class
     *
     *          <li> the caller's class loader is not the same as or an
     *          ancestor of the class loader for the current class and
     *          invocation of {@link SecurityManager#checkPackageAccess
     *          s.checkPackageAccess()} denies access to the package
     *          of this class
     *
     *          </ul>
     *
     * @jls 8.2 Class Members
     * @jls 8.4 Method Declarations
     * @since JDK1.1
     */
    @CallerSensitive
    public Method[] getDeclaredMethods() throws SecurityException {
        checkMemberAccess(Member.DECLARED, Reflection.getCallerClass(), true);
        return copyMethods(privateGetDeclaredMethods(false));
    }


/**
     * Returns an array containing {@code Method} objects reflecting all the
     * public methods of the class or interface represented by this {@code
     * Class} object, including those declared by the class or interface and
     * those inherited from superclasses and superinterfaces.
     *
     * <p> If this {@code Class} object represents a type that has multiple
     * public methods with the same name and parameter types, but different
     * return types, then the returned array has a {@code Method} object for
     * each such method.
     *
     * <p> If this {@code Class} object represents a type with a class
     * initialization method {@code <clinit>}, then the returned array does
     * <em>not</em> have a corresponding {@code Method} object.
     *
     * <p> If this {@code Class} object represents an array type, then the
     * returned array has a {@code Method} object for each of the public
     * methods inherited by the array type from {@code Object}. It does not
     * contain a {@code Method} object for {@code clone()}.
     *
     * <p> If this {@code Class} object represents an interface then the
     * returned array does not contain any implicitly declared methods from
     * {@code Object}. Therefore, if no methods are explicitly declared in
     * this interface or any of its superinterfaces then the returned array
     * has length 0. (Note that a {@code Class} object which represents a class
     * always has public methods, inherited from {@code Object}.)
     *
     * <p> If this {@code Class} object represents a primitive type or void,
     * then the returned array has length 0.
     *
     * <p> Static methods declared in superinterfaces of the class or interface
     * represented by this {@code Class} object are not considered members of
     * the class or interface.
     *
     * <p> The elements in the returned array are not sorted and are not in any
     * particular order.
     *
     * @return the array of {@code Method} objects representing the
     *         public methods of this class
     * @throws SecurityException
     *         If a security manager, <i>s</i>, is present and
     *         the caller's class loader is not the same as or an
     *         ancestor of the class loader for the current class and
     *         invocation of {@link SecurityManager#checkPackageAccess
     *         s.checkPackageAccess()} denies access to the package
     *         of this class.
     *
     * @jls 8.2 Class Members
     * @jls 8.4 Method Declarations
     * @since JDK1.1
     */
    @CallerSensitive
    public Method[] getMethods() throws SecurityException {
        checkMemberAccess(Member.PUBLIC, Reflection.getCallerClass(), true);
        return copyMethods(privateGetPublicMethods());
    }

同理拓展getDeclaredFields 方法獲取當前類的所有變量，而getFields方法獲取該類及其父類的所有public成員變量。