如何获取已经在另一个 class 中设置的实例值？

Question

我是 Java 的新手。 我有 3 个类：1-DataHolder 2-SetToDateHolder 3-GetFromDataHolder； In the "SetToDateHolder" class, I set the value to dataholder object, and I trying to access it in the "GetFromDataHolder" class, but it got null value, I know it happens because of new instance created. 你能帮我意识到我可以得到我在另一个 class 中设置的实例的值。

这些是类：

public class DataHolder {

    private String myName;

    public String getMyName() {
        return myName;
    }

    public void setMyName(String myName) {
        this.myName = myName;
    }
}

public class SetToDataHolder {

    public static void main(String[] args) {
        DataHolder dataHolder = new DataHolder();
        dataHolder.setMyName("Wesley");
    }

}

public class GetFromDataHolder{
    
    public static void main(String[] args) {
        DataHolder dataHolder = new DataHolder();
        System.out.println(dataHolder.getMyName());
    }

}

Answer 1

我真的不明白为什么你需要 2 个额外的类，因为你的 DataHolder class 中已经有了 getter / setter，但这里是你应该如何继续你的逻辑：

public class DataHolder {

    private String myName;

    public String getMyName() {
        return myName;
    }

    public void setMyName(String myName) {
        this.myName = myName;
    }
}

public class SetToDataHolder {
    
    private DataHolder dataHolder;

    public SetToDataHolder(DataHolder dataHolder){
        this.dataHolder = dataHolder;
    }

    public void setMyName(String myName) {
        this.dataHolder.setMyName(myName);
    }
}

public class GetFromDataHolder{
    
    private DataHolder dataHolder;

    public GetFromDataHolder(DataHolder dataHolder){
        this.dataHolder = dataHolder;
    }

    public String getMyName() {
        this.dataHolder.getMyName();
    }
}

public class MainClass{
    
    public static void main(String[] args){
        DataHolder dataHolder = new DataHolder();

        SetToDataHolder setToDataHolder = new SetToDataHolder(dataHolder);
        setToDataHolder.setMyName("Wesley");

        GetFromDataHolder getFromDataHolder = new GetFromDataHolder(dataHolder);
        System.out.println(getFromDataHolder.getMyName());
    }
}

这个想法是您的 SetToDataHolder 和 GetFromDataHolder 可以访问相同的 DataHolder 实例。