創建全局列表對象Java

Question

我想創建一個全局列表，可以訪問我的包的所有類。

例如，下面的類創建對象

public class Class2 { 

protected String one, two, three; 

public void newItem(String one, String two, String three) { 

    this.one = one; 
    this.two = two; 
    this.three = three; 
} 

public String getInfo() { 

    return one + "," + two + "," + three; 
} 

我想從另一個類創建對象的Class2的列表（假設Class1.java），我想該列表可從其他類，讓我們說Class3.java。

行爲應該像數據庫一樣，其中一個類創建List和其他類讀取該列表以執行一些本地操作。

Answer 1

無需任何額外的依賴和單身簡單的解決方案：

//Class which represents this "data storage" of yours. You can even have multiple instances of it simultaneously if you need 
class Database { 
    //Some data the DB contains 
    private List<MyEntity> entities = new ArrayList<>(); 

    //Way to read the stored data 
    public List<MyEntity> getEntities() { 
     return entities; 
    } 

    //Way to add new data 
    public void addEntity(MyEntity newEntity) { 
     entities.add(newEntity); 
    } 
} 

//Some working class, which fills the database with information 
class EntityCreator { 
    private final Database db; 

    //Each working class attaches itself to specific database instance. Therefore, you need to pass that instance through the constructor and save it for later job 
    public EntityCreator(Database operationalDb) { 
     this.db = operationalDb; 
    } 

    public void writeSomeData() { 
     for (.....) { 
      db.addEntity(new MyEntity(...)); 
     } 
    } 
} 

//Some working class, which depends on information saved in database 
class EntityReader { 
    private final Database db; 

    //Each working class attaches itself to specific database instance. Therefore, you need to pass that instance through the constructor and save it for later job 
    public EntityCreator(Database operationalDb) { 
     this.db = operationalDb; 
    } 

    public void doSomeWork() { 
     for (MyEntity e : db.getEntities()) { 
      doStuff(e); 
     } 
    } 
} 

//Example of the full workflow 
class MainClass { 
    public static void main(String[] args) { 
     Database db = new Database(); 
     EntityCreator creator = new EntityCreator(db); 
     EntityReader reader = new EntityReader(db); 

     creator.writeSomeData(); 
     reader.doSomeWork(); 
    } 
} 

而且，值得注意的，它不是線程安全的，但它給後面的佈線不使用DI框架一起相依的主要思想。