public class ClassB{
    //ClassB 不能序列化，因为没有实现Serializable接口
    private String str;
    public ClassB(){
        //default constructor
    }

    public ClassB(String str){
        this.str = str;
    }
}

import java.io.Serializable;

public class ClassC implements Serializable{
    private ClassB b;
    public ClassC(){
        //default constructor
    }

    public ClassC(String str){
        b = new ClassB(str);
    }

    public ClassB getClassB(){
        return b;
    }
}

import java.io.File;
import java.io.FileOutputStream;
import java.io.FileInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedInputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;

public class Test{
    public static void main(String[] args)throws Exception{
        File file = new File("aa.bin");
        ObjectOutputStream outStream = new ObjectOutputStream(
            new BufferedOutputStream(
            new FileOutputStream(file)));
        outStream.writeObject(new ClassC("ricky"));
        outStream.close();

        ObjectInputStream inStream = new ObjectInputStream(
            new BufferedInputStream(
            new FileInputStream(file)));
        inStream.readObject();
    }
}

---------- java ----------
Exception in thread "main" java.io.NotSerializableException: ClassB
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1156)
    at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1509)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1474)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1392)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1150)
    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:326)
    at Test.main(Test.java:15)

输出完成 (耗时: 3 秒) - 正常终止