instanceof, isinstance,isAssignableFrom说明

博客介绍了Java中几个对象实例检测的方法。instanceof用于检测左边对象是否为右边类或接口的实例化,若左边为null则返回false;isInstance是Class类的方法,功能与instanceof类似;isAssignableFrom可判断调用方法的类或接口与参数类或接口的关系。

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instanceof:检测左边对象是不是右边类或接口的实例化。如果左边的是null则直接返回false。

obj instanceof 类

例子:

String s = new String("aaa");
if(s instanceof String){
    System.out.println("true");
}
输出true

isInstance:Class类的方法,判断obj是不是该类或接口的实例化。和instanceof类似。

类.class.isInstance(obj)

String s = new String("aaa");
if(String.class.isInstance(s)){
    System.out.println("true");
}
输出true

isAssignableFrom:如果调用这个方法的class或接口 与 参数cls表示的类或接口相同,或者是参数cls表示的类或接口的父类,则返回true。 

类.class.isAssignableFrom(类2.class)

System.out.println(ArrayList.class.isAssignableFrom(Object.class));
输出false
System.out.println(Object.class.isAssignableFrom(ArrayList.class));
输出true

 

package com.example.kucun2.entity.data; import android.util.Log; import androidx.annotation.NonNull; import com.google.gson.Gson; import java.io.IOException; import java.lang.reflect.Method; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; import java.util.ArrayList; import java.util.Arrays; import java.util.Collection; import java.util.HashSet; import java.util.Iterator; import java.util.List; import java.util.ListIterator; import java.util.Set; import okhttp3.Call; import okhttp3.Callback; import okhttp3.MediaType; import okhttp3.OkHttpClient; import okhttp3.Request; import okhttp3.RequestBody; import okhttp3.Response; /** * 支持数据变更自动同步的泛型集合类 * @param <T> 继承自 SynchronizableEntity 的实体类型 */ public class SynchronizedList<T extends SynchronizableEntity> implements List<T> { private final List<T> list = new ArrayList<>(); private final OkHttpClient client = new OkHttpClient(); private static final Gson gson = new Gson(); private static final MediaType JSON = MediaType.get("application/json; charset=utf-8"); private final Class<T> entityClass; // 类型标记 // 添加批量操作模式标志 private boolean batchMode = false; // 属性变更监听器 private final List<PropertyChangeListener<T>> listeners = new ArrayList<>(); public SynchronizedList(Class<T> entityClass) { Type superClass = getClass().getGenericSuperclass(); ParameterizedType type = (ParameterizedType) superClass; Type[] typeArgs = type.getActualTypeArguments(); this.entityClass = (Class<T>) typeArgs[0]; } // 安全的类型转换方法 private T safeCast(Object o) { if (o != null && entityClass.isInstance(o)) { return entityClass.cast(o); } return null; } public interface PropertyChangeListener<T> { void onPropertyChange(T entity, String propertyName, Object oldValue, Object newValue); } public void addPropertyChangeListener(PropertyChangeListener<T> listener) { listeners.add(listener); } public void removePropertyChangeListener(PropertyChangeListener<T> listener) { listeners.remove(listener); } // 添加方法来获取原始对象 @SuppressWarnings("unchecked") public T getOriginal(T proxy) { if (proxy == null) return null; // 检查是否为代理对象 if (java.lang.reflect.Proxy.isProxyClass(proxy.getClass())) { try { java.lang.reflect.InvocationHandler handler = java.lang.reflect.Proxy.getInvocationHandler(proxy); if (handler instanceof IProxyHandler) { //没有IProxyHandler类 return ((IProxyHandler) handler).getOriginal(); } } catch (Exception e) { Log.e("SynchronizedList", "Failed to get proxy handler", e); } } return proxy; } /** * 同步实体到后端 * * @param entity 要同步的实体 */ private void syncEntity(T entity) { if (batchMode) return; String operation = "add"; T originalEntity = getOriginal(entity); String endpoint = originalEntity.getEndpoint(operation); String json = gson.toJson(originalEntity); RequestBody body = RequestBody.create(json, JSON); Request request = new Request.Builder() .url(endpoint) .method(getHttpMethod(operation), body) .build(); client.newCall(request).enqueue(new Callback() { @Override public void onFailure(@NonNull Call call, @NonNull IOException e) { Log.e("SynchronizedList", "同步失败: " + entity.getClass().getSimpleName(), e); } @Override public void onResponse(@NonNull Call call, @NonNull Response response) { if (!response.isSuccessful()) { Log.e("SynchronizedList", "同步失败: " + response.code() + " - " + response.message()); } response.close(); } }); } // 添加用于批量操作的方法 public void beginBatch() { this.batchMode = true; } public void endBatch() { this.batchMode = false; // 批量结束后触发一次全量同步 syncAllEntities(); } private void syncAllEntities() { for (T entity : list) { syncEntity(entity); } } private String getHttpMethod(String operation) { switch (operation) { case "add": return "POST"; case "update": return "PUT"; case "delete": return "DELETE"; default: return "POST"; } } // 获取类实现的所有接口(包括父类接口) private Class<?>[] getInterfaces(Class<?> clazz) { Set<Class<?>> interfaces = new HashSet<>(); while (clazz != null) { interfaces.addAll(Arrays.asList(clazz.getInterfaces())); clazz = clazz.getSuperclass(); } return interfaces.toArray(new Class<?>[0]); } /** * 创建代理对象,用于监听属性变更 */ private T createProxy(T original) { if (!entityClass.isInstance(original)) { throw new IllegalArgumentException("Invalid entity type"); } return (T) java.lang.reflect.Proxy.newProxyInstance( original.getClass().getClassLoader(), getInterfaces(original.getClass()), new EntityProxyHandler(original) ); // if (!entityClass.isInstance(original)) { // throw new IllegalArgumentException("Invalid entity type"); // } // // 这里使用动态代理模式监听setter方法调用 // return (T) java.lang.reflect.Proxy.newProxyInstance( // original.getClass().getClassLoader(), // original.getClass().getInterfaces(), // (proxy, method, args) -> { // // 只拦截setter方法 // if (method.getName().startsWith("set") && args.length == 1) { // String propertyName = method.getName().substring(3); // propertyName = propertyName.substring(0, 1).toLowerCase() + propertyName.substring(1); // // // 获取旧值 // Object oldValue = original.getClass() // .getMethod("get" + propertyName.substring(0, 1).toUpperCase() + propertyName.substring(1)) // .invoke(original); // // // 调用原始方法 // Object result = method.invoke(original, args); // // // 触发监听器 // for (PropertyChangeListener<T> listener : listeners) { // listener.onPropertyChange(original, propertyName, oldValue, args[0]); // } // // // 自动同步到后端 // syncEntity(original); // return result; // } // return method.invoke(original, args); // } // ); } // 以下是List接口的实现 @Override public int size() { return list.size(); } @Override public boolean isEmpty() { return list.isEmpty(); } @Override public boolean contains(Object o) { return list.contains(o); } @NonNull @Override public Iterator<T> iterator() { return list.iterator(); } @NonNull @Override public Object[] toArray() { return list.toArray(); } @NonNull @Override public <T1> T1[] toArray(@NonNull T1[] a) { return list.toArray(a); } @Override public boolean add(T t) { T proxy = createProxy(t); boolean result = list.add(proxy); if (!batchMode) { syncEntity(proxy); } return result; // 添加时创建代理 } @Override public boolean remove(Object o) { T entity = safeCast(o); if (entity != null) { syncEntity((T) entity); // 删除前同步 } return list.remove(o); } @Override public boolean containsAll(@NonNull Collection<?> c) { return list.containsAll(c); } @Override public boolean addAll(@NonNull Collection<? extends T> c) { boolean modified = false; for (T t : c) { modified |= add(t); } return modified; } @Override public boolean addAll(int index, @NonNull Collection<? extends T> c) { for (T t : c) { add(index++, t); } return true; } @Override public boolean removeAll(@NonNull Collection<?> c) { for (Object o : c) { T entity = safeCast(o); if (entity != null) { syncEntity(entity); } } return list.removeAll(c); } @Override public boolean retainAll(@NonNull Collection<?> c) { List<T> toRemove = new ArrayList<>(); for (T t : list) { if (!c.contains(t)) { toRemove.add(t); } } // 使用安全转换 for (T entity : toRemove) { syncEntity(entity); } return list.retainAll(c); } @Override public void clear() { for (T t : list) { syncEntity(t); // 清空前同步 } list.clear(); } @Override public T get(int index) { return list.get(index); } @Override public T set(int index, T element) { T old = list.set(index, createProxy(element)); if (old != null) { syncEntity(old); // 替换旧元素前同步 } return old; } @Override public void add(int index, T element) { list.add(index, createProxy(element)); } @Override public T remove(int index) { T removed = list.remove(index); if (removed != null) { syncEntity(removed); // 删除前同步 } return removed; } @Override public int indexOf(Object o) { return list.indexOf(o); } @Override public int lastIndexOf(Object o) { return list.lastIndexOf(o); } @NonNull @Override public ListIterator<T> listIterator() { return list.listIterator(); } @NonNull @Override public ListIterator<T> listIterator(int index) { return list.listIterator(index); } @NonNull @Override public List<T> subList(int fromIndex, int toIndex) { return list.subList(fromIndex, toIndex); } // 触发属性变更通知 private void firePropertyChange(T entity, String propertyName, Object oldValue, Object newValue) { for (PropertyChangeListener<T> listener : listeners) { listener.onPropertyChange(entity, propertyName, oldValue, newValue); } } // 修改代理处理器以支持获取原始对象 /* 完整的 EntityProxyHandler 实现 */ private class EntityProxyHandler implements IProxyHandler/*报错*/, java.lang.reflect.InvocationHandler { private final T original; public EntityProxyHandler(T original) { this.original = original; } @Override public T getOriginal() { return original; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { // 处理 setter 方法 if (method.getName().startsWith("set") && args.length == 1) { String propertyName = method.getName().substring(3); propertyName = propertyName.substring(0, 1).toLowerCase() + propertyName.substring(1); // 获取旧值 Object oldValue = getPropertyValue(propertyName); // 调用原始方法 Object result = method.invoke(original, args); // 触发属性变更监听 firePropertyChange(original, propertyName, oldValue, args[0]); // 批量模式下不自动同步 if (!batchMode) { syncEntity(original); } return result; } // 特殊处理 getOriginal() 方法 if ("getOriginal".equals(method.getName()) && method.getParameterCount() == 0) { return original; } return method.invoke(original, args); } private Object getPropertyValue(String propertyName) { String getterName = "get" + propertyName.substring(0, 1).toUpperCase() + propertyName.substring(1); try { Method getter = original.getClass().getMethod(getterName); return getter.invoke(original); } catch (Exception e) { Log.e("ProxyHandler", "Failed to get property value: " + propertyName, e); return null; } } } }package com.example.kucun2.entity.data; import android.content.Context; import android.util.Log; import com.example.kucun2.entity.*; import com.example.kucun2.function.MyAppFnction; import com.google.gson.Gson; import com.google.gson.reflect.TypeToken; import java.io.IOException; import java.lang.reflect.Field; import java.lang.reflect.Method; import java.lang.reflect.Type; import java.util.*; import okhttp3.Call; import okhttp3.Callback; import okhttp3.OkHttpClient; import okhttp3.Request; import okhttp3.Response; public class Data { // 数据集合声明(保持原有属性名不变) public static SynchronizedList<Bancai> bancais = new SynchronizedList<>(Bancai.class); public static SynchronizedList<Caizhi> caizhis = new SynchronizedList<>(Caizhi.class); public static SynchronizedList<Mupi> mupis = new SynchronizedList<>(Mupi.class); public static SynchronizedList<Chanpin> chanpins = new SynchronizedList<>(Chanpin.class); public static SynchronizedList<Chanpin_Zujian> chanpinZujians = new SynchronizedList<>(Chanpin_Zujian.class); public static SynchronizedList<Dingdan> dingdans = new SynchronizedList<>(Dingdan.class); public static SynchronizedList<Dingdan_Chanpin> dingdanChanpins = new SynchronizedList<>(Dingdan_Chanpin.class); public static SynchronizedList<Dingdan_Bancai> dingdanBancais = new SynchronizedList<>(Dingdan_Bancai.class); public static SynchronizedList<Kucun> kucuns = new SynchronizedList<>(Kucun.class); public static SynchronizedList<Zujian> zujians = new SynchronizedList<>(Zujian.class); public static SynchronizedList<User> users = new SynchronizedList<>(User.class); public static SynchronizedList<Jinhuo> jinhuoList = new SynchronizedList<>(Jinhuo.class); private static final Gson gson = new Gson(); private static final OkHttpClient client = new OkHttpClient(); private static final String TAG = "DataLoader"; // 加载所有数据的方法 public static void loadAllData(Context context, LoadDataCallback callback) { // 开始批量模式 for (SynchronizedList<?> list : getAllSyncLists()) { list.beginBatch(); } String url = MyAppFnction.getStringResource("String", "url") + MyAppFnction.getStringResource("String", "url_all"); Request request = new Request.Builder() .url(url) .build(); client.newCall(request).enqueue(new Callback() { @Override public void onFailure(Call call, IOException e) { Log.e(TAG, "Failed to load data", e); if (callback != null) callback.onFailure(); } @Override public void onResponse(Call call, Response response) throws IOException { parseAndAssignData(response.body().string(), context);//参数不对报错 // 结束批量模式(会触发一次全量同步) for (SynchronizedList<?> list : getAllSyncLists()) { list.endBatch(); } if (callback != null) callback.onSuccess(); } }); } // 获取所有同步列表的方法 private static List<SynchronizedList<?>> getAllSyncLists() { return Arrays.asList(bancais, caizhis, mupis, chanpins, chanpinZujians, dingdans, dingdanChanpins, dingdanBancais, kucuns, zujians, users, jinhuoList); } // 解析并赋值数据 private static void parseAndAssignData(String jsonData, Context context, LoadDataCallback callback) { // 创建包含所有数据类型的TypeToken Type informationType = new TypeToken<Information<AllDataResponse>>(){}.getType(); Information<AllDataResponse> information = gson.fromJson(jsonData, informationType); if (information == null || information.getData() == null || information.getStatus() != 200) { Log.e(TAG, "Invalid response data"); if (callback != null) callback.onFailure(); return; } AllDataResponse allData = information.getData(); // 赋值到对应的列表(使用安全方法保持已有引用) updateList(bancais, allData.bancais); updateList(caizhis, allData.caizhis); updateList(mupis, allData.mupis); updateList(chanpins, allData.chanpins); updateList(chanpinZujians, allData.chanpin_zujians); updateList(dingdans, allData.dingdans); updateList(dingdanChanpins, allData.dingdan_chanpins); updateList(dingdanBancais, allData.dingdan_bancais); updateList(kucuns, allData.kucuns); updateList(zujians, allData.zujians); updateList(users, allData.users); updateList(jinhuoList, allData.jinhuos); resolveReferences(); if (callback != null) callback.onSuccess(); } // 更新列表内容但保持对象引用不变 private static <T> void updateList(List<T> existingList, List<T> newList) { if (newList == null) return; existingList.clear(); for (T item : newList) { existingList.add(item); // 会被包装成代理对象 } } // 解析对象间的引用关系(使用ID关联) // 改进的引用解析方法 private static void resolveReferences() { // 创建全局对象映射 Map<Integer, EntityClassGrassrootsid> globalMap = new HashMap<>(); // 填充全局映射表 addToGlobalMap(globalMap, bancais); addToGlobalMap(globalMap, caizhis); addToGlobalMap(globalMap, mupis); addToGlobalMap(globalMap, chanpins); addToGlobalMap(globalMap, zujians); addToGlobalMap(globalMap, dingdans); addToGlobalMap(globalMap, kucuns); addToGlobalMap(globalMap, users); // 解析所有实体的引用 resolveListReferences(bancais, globalMap); resolveListReferences(kucuns, globalMap); resolveListReferences(dingdanChanpins, globalMap); resolveListReferences(chanpinZujians, globalMap); resolveListReferences(dingdanBancais, globalMap); resolveListReferences(jinhuoList, globalMap); } // 添加对象到全局映射表 private static void addToGlobalMap(Map<Integer, EntityClassGrassrootsid> map, SynchronizedList<?> list) { for (Object item : list) { Object original = getOriginalFromList(list, item); if (original instanceof EntityClassGrassrootsid) { EntityClassGrassrootsid entity = (EntityClassGrassrootsid) original; map.put(entity.getId(), entity); } } } // 解析列表中所有实体的引用 private static void resolveListReferences(SynchronizedList<?> list, Map<Integer, EntityClassGrassrootsid> globalMap) { for (Object item : list) { Object original = getOriginalFromList(list, item); resolveEntityReferences(original, globalMap); } } // 安全获取原始对象(无需类型转换) @SuppressWarnings("unchecked") private static <T> T getOriginalFromList(SynchronizedList<?> list, Object item) { try { // 使用反射调用getOriginal方法 Method getOriginal = list.getClass().getMethod("getOriginal", Object.class); return (T) getOriginal.invoke(list, item); } catch (Exception e) { Log.e("Data", "Failed to get original object", e); return (T) item; } } //解析集合中的引用 private static void resolveCollectionReferences(Collection<?> collection, Map<Integer, EntityClassGrassrootsid> globalMap) { for (Object item : collection) { if (item instanceof EntityClassGrassrootsid) { EntityClassGrassrootsid ref = (EntityClassGrassrootsid) item; EntityClassGrassrootsid resolved = globalMap.get(ref.getId()); if (resolved != null && ref.getClass().isInstance(resolved)) { // 注意:直接替换集合元素需要特殊处理 // 实际项目应考虑使用CopyOnWrite集合或创建新集合 if (collection instanceof List) { int index = ((List<?>) collection).indexOf(ref); if (index != -1) { try { ((List<Object>) collection).set(index, resolved); } catch (Exception e) { Log.e("Data", "Failed to update collection", e); } } } } } } } // 解析单个实体的引用 private static void resolveEntityReferences(Object entity, Map<Integer, EntityClassGrassrootsid> globalMap) { if (entity == null) return; Class<?> clazz = entity.getClass(); for (Field field : clazz.getDeclaredFields()) { try { field.setAccessible(true); // 处理基本类型字段 if (EntityClassGrassrootsid.class.isAssignableFrom(field.getType())) { EntityClassGrassrootsid ref = (EntityClassGrassrootsid) field.get(entity); if (ref != null && ref.getId() != null) { EntityClassGrassrootsid resolved = globalMap.get(ref.getId()); if (resolved != null && field.getType().isInstance(resolved)) { field.set(entity, resolved); } } } // 处理集合类型字段 else if (Collection.class.isAssignableFrom(field.getType())) { Collection<?> collection = (Collection<?>) field.get(entity); if (collection != null) { resolveCollectionReferences(collection, globalMap); } } } catch (Exception e) { Log.e("Data", "Error resolving field: " + field.getName(), e); } } } // 创建ID到对象的映射 private static <T extends EntityClassGrassrootsid> Map<Integer, T> createIdMap(List<T> list) { Map<Integer, T> map = new HashMap<>(); for (T item : list) { map.put(item.getId(), item); } return map; } // 回调接口 public interface LoadDataCallback { void onSuccess(); void onFailure(); } private static void resolveFields(Object entity, Map<Integer, EntityClassGrassrootsid> globalMap) { for (Field field : entity.getClass().getDeclaredFields()) { if (EntityClassGrassrootsid.class.isAssignableFrom(field.getType())) { try { field.setAccessible(true); EntityClassGrassrootsid ref = (EntityClassGrassrootsid) field.get(entity); if (ref != null) { EntityClassGrassrootsid resolved = globalMap.get(ref.getId()); if (resolved != null && field.getType().isAssignableFrom(resolved.getClass())) { field.set(entity, resolved); } } } catch (Exception e) { Log.e("Data", "Error resolving reference", e); } } } } // 内部类用于解析JSON响应 public static class AllDataResponse { public List<Bancai> bancais; public List<Caizhi> caizhis; public List<Mupi> mupis; public List<Chanpin> chanpins; public List<Chanpin_Zujian> chanpin_zujians; public List<Dingdan> dingdans; public List<Dingdan_Chanpin> dingdan_chanpins; public List<Dingdan_Bancai> dingdan_bancais; public List<Kucun> kucuns; public List<Zujian> zujians; public List<User> users; public List<Jinhuo> jinhuos; } }
最新发布
06-10
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