getField()与getDeclaredField()的区别

分手后的思念是犯贱 2023-02-10 05:06 13阅读 0赞

Java的反射机制中，用Class的getField(String name)或getDelaredField(String name)可以得到目标类的指定属性，返回类型是Field。

在看它们的区别之前先看下它们的源码(英文部分自己翻译了下)：

/** * Returns a {@code Field} object that reflects the specified public member * field of the class or interface represented by this {@code Class} * object. The {@code name} parameter is a {@code String} specifying the * simple name of the desired field. * * 返回一个域对象，反射出这个类对象所代表的类或接口的指定的Public 域成员。 * 名称参数是由字符串所指定的期望域的简单名称 * The field to be reflected is determined by the algorithm that * follows. Let C be the class or interface represented by this object: * * 这个域被如下的算法所决定。C是这个对象所代表的类或者接口 * <OL> * <LI> If C declares a public field with the name specified, that is the * field to be reflected.</LI> * 如果C声明一个由指定名称的公共域，那就是要被反射的域 * <LI> If no field was found in step 1 above, this algorithm is applied * recursively to each direct superinterface of C. The direct * superinterfaces are searched in the order they were declared.</LI> * 如果在步骤1中没有域被找到，这个算法将递归应用到每个C的父接口中。直接的父接口 * 将由声明顺序遍历查找。 * <LI> If no field was found in steps 1 and 2 above, and C has a * superclass S, then this algorithm is invoked recursively upon S. * If C has no superclass, then a {@code NoSuchFieldException} * is thrown.</LI> * </OL> * 如果在步骤1和步骤2中，没有域被找到，C有一个父类型S，然后这个算法将被在S上递归调用。 * 如果C没有父类，则会抛出NoSuchFieldException的异常 * If this {@code Class} object represents an array type, then this * method does not find the {@code length} field of the array type. * * 如果这个类对象代表一个数组类型，那么这个方法将找不到这个数组类型的length域 * @param name the field name * @return the {@code Field} object of this class specified by * {@code name} * @throws NoSuchFieldException if a field with the specified name is * not found. * @throws NullPointerException if {@code name} is {@code null} * @throws SecurityException * If a security manager, s, 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. * * @since JDK1.1 * @jls 8.2 Class Members * @jls 8.3 Field Declarations */
 @CallerSensitive
 public Field getField(String name)
 throws NoSuchFieldException, SecurityException { 
 checkMemberAccess(Member.PUBLIC, Reflection.getCallerClass(), true);
 Field field = getField0(name);
 if (field == null) { 
 throw new NoSuchFieldException(name);
 }
 return field;
 }

/** * Returns a {@code Field} object that reflects the specified declared * field of the class or interface represented by this {@code Class} * object. The {@code name} parameter is a {@code String} that specifies * the simple name of the desired field. * *返回一个域对象，反射出这个类对象所代表的类或接口所声明的所有域成员。 * 名称参数是由字符串所指定的期望域的简单名称 * If this {@code Class} object represents an array type, then this * method does not find the {@code length} field of the array type. * *如果这个类对象代表一个数组类型，那么这个方法将找不到这个数组类型的length域 * @param name the name of the field * @return the {@code Field} object for the specified field in this * class * @throws NoSuchFieldException if a field with the specified name is * not found. * @throws NullPointerException if {@code name} is {@code null} * @throws SecurityException * If a security manager, s, 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 field * * <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> * * @since JDK1.1 * @jls 8.2 Class Members * @jls 8.3 Field Declarations */
 @CallerSensitive
 public Field getDeclaredField(String name)
 throws NoSuchFieldException, SecurityException { 
 checkMemberAccess(Member.DECLARED, Reflection.getCallerClass(), true);
 Field field = searchFields(privateGetDeclaredFields(false), name);
 if (field == null) { 
 throw new NoSuchFieldException(name);
 }
 return field;
 }

getField(String name)只能获取public的字段，包括父类的；

而getDeclaredField(String name)能获取自己声明的各种字段，包括public，protected，private。