在JAVA中使用gson从/到Json读取/写入不同对象的数组列表

我需要保存并加载Json文件，其中包含一个ArrayList对象。 数组列表中的对象：单项式多项式和ComplexFunction

说明： 在这个项目中，我有3个主要对象和1个对象，它们将所有对象保存在一个列表中。 （所有这些实现了“功能”接口）

单体-从两个字段构建双系数，整数幂

多项式-单项式的数组列表

ComplexFunction—保存两个函数对象（左侧和右侧）以及它们之间的操作（time div…）

我需要再构建一个对象，Functions\uGUI，它可以在一个集合中包含所有这些“函数”。。。我使用了名为列表的ArrayList。此对象需要有两个主要功能：

saveToFile-使用Gson将此GUI保存为具有给定文件名的JSON

我的代码：

public void saveToFile(String file) throws IOException {
        try 
        {
            Gson gson = new Gson();
            String json = gson.toJson(this);
            System.out.println(json);
            String file_name = file+".json";
            PrintWriter pw = new PrintWriter(new File(file_name));
            pw.write(json);
            pw.close();
        } 
        catch (FileNotFoundException e) 
        {
            e.printStackTrace();

        }

    }

public void initFromFile(String file) throws IOException {
        try {
            Gson gson = new Gson();
            JsonReader reader =  new JsonReader (new FileReader(file));
            Functions_GUI tg1 = gson.fromJson(reader, Functions_GUI.class);
            this.list=tg1.list;
        }catch (Exception e) {
            throw new RuntimeException(e);
        }

    }

完成此操作后，我将获得此文件：

[
{"PloynomList":[]},
{"CF_LeftFunction":
    {"PloynomList":[
        {"Coefficient":1.0,"Power":3},
        {"Coefficient":-13.0,"Power":2},
        {"Coefficient":-2.0,"Power":0}]},
"CF_RightFunction":{
        "PloynomList":[
            {"Coefficient":1.0,"Power":1},
            {"Coefficient":-2.0,"Power":0}]},
"CF_Operation":"Divid"},
{"PloynomList":[
    {"Coefficient":1.0,"Power":3},
    {"Coefficient":-13.0,"Power":2},
    {"Coefficient":-2.0,"Power":0}]},
{"PloynomList":[
    {"Coefficient":1.0,"Power":4},
    {"Coefficient":-2.0,"Power":0}]},
{"PloynomList":[
    {"Coefficient":1.0,"Power":1},
    {"Coefficient":-2.0,"Power":0}]},
{"PloynomList":[
    {"Coefficient":12.0,"Power":1},
    {"Coefficient":-2.0,"Power":0}]},
{"PloynomList":[
    {"Coefficient":-2.0,"Power":7},
    {"Coefficient":1.0,"Power":1}]}
] 

initFromFile-获取一个JSON文件并从中初始化一个GUI对象 我的代码：

public void saveToFile(String file) throws IOException {
        try 
        {
            Gson gson = new Gson();
            String json = gson.toJson(this);
            System.out.println(json);
            String file_name = file+".json";
            PrintWriter pw = new PrintWriter(new File(file_name));
            pw.write(json);
            pw.close();
        } 
        catch (FileNotFoundException e) 
        {
            e.printStackTrace();

        }

    }

public void initFromFile(String file) throws IOException {
        try {
            Gson gson = new Gson();
            JsonReader reader =  new JsonReader (new FileReader(file));
            Functions_GUI tg1 = gson.fromJson(reader, Functions_GUI.class);
            this.list=tg1.list;
        }catch (Exception e) {
            throw new RuntimeException(e);
        }

    }

您可以看到，上面的文件是使用所有对象的所有字段创建的。。 但是，当我尝试读取同一文件并从中创建新函数\u GUI时，会出现以下错误：

Exception in thread "main" java.lang.RuntimeException: java.lang.RuntimeException: Unable to invoke no-args constructor for interface Ex1.function. Register an InstanceCreator with Gson for this type may fix this problem.
    at Ex1.Functions_GUI.initFromFile(Functions_GUI.java:125)
    at Ex1.MainTest.main(MainTest.java:183)
Caused by: java.lang.RuntimeException: Unable to invoke no-args constructor for interface Ex1.function. Register an InstanceCreator with Gson for this type may fix this problem.
    at com.google.gson.internal.ConstructorConstructor$8.construct(ConstructorConstructor.java:167)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:162)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:81)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:60)
    at com.google.gson.Gson.fromJson(Gson.java:795)
    at Ex1.Functions_GUI.initFromFile(Functions_GUI.java:122)
    ... 1 more
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.google.gson.internal.UnsafeAllocator$1.newInstance(UnsafeAllocator.java:48)
    at com.google.gson.internal.ConstructorConstructor$8.construct(ConstructorConstructor.java:164)
    ... 7 more
Caused by: java.lang.InstantiationException: Ex1.function
    at sun.misc.Unsafe.allocateInstance(Native Method)
    ... 13 more

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请告知

的可能重复。您能展示一下您的

POJO

类吗。看起来，

Gson

不知道在发现接口时使用哪个实现。