Question

我希望程序打印方法readA()和readB()的回复，但我收到来自main的错误，指出valueB需要String,String因为我的构造函数GenericMemoryCell()。但是如果我需要通过构造函数接收和存储2个参数，那么我是否必须向构造函数发送2个参数，如下所示？我怎样才能只将1个字符串分配给valueB？

public class GenericMemoryCell<T>{

    public static void main(String[] args) {
        GenericMemoryCell<String> valueA = new GenericMemoryCell<String>("1", "1"); 
        GenericMemoryCell<String> valueB = new GenericMemoryCell<String>("1"); 
        System.out.println("storedValueA: " + valueA.readA());
        System.out.println("storedValueB: " + valueB.readB());
    }

    public GenericMemoryCell(T storedValueA, T storedValueB)
    { this.storedValueA = storedValueA; this.storedValueB = storedValueB; writeA(storedValueA); writeB(storedValueB); }

    public T readA()
    { return storedValueA; }

    public T readB()
    { return storedValueB; }

    private T storedValueA, storedValueB;
}

Answer 1

如果要创建传递单个参数的GenericMemoryCell，则需要添加带有单个参数的第二个构造函数。

以下是单个param构造函数的示例，它只调用两个param构造函数，为第二个值传递null：

public GenericMemoryCell(T storedValueA, T storedValueB) {
    ...
}

public GenericMemoryCell(T storedValueA) {
    this(storedValueA, null);
}

Answer 2

以下是通过使用单个参数再创建一个构造函数，仅将1个String分配给valueB：

public GenericMemoryCell(T storedValueB) {
    this.storedValueB = storedValueB;       
}

所以，现在你的班级如下所示。我已经编辑了一些地方来改进它。与包含两个参数的构造函数一样，无需调用：writeA(storedValueA)和writeB(storedValueB)。

GenericMemoryCell.java

    public class GenericMemoryCell<T> {

    public static void main(String[] args) {
        GenericMemoryCell<String> valueA = new GenericMemoryCell<String>("1", "2");
        GenericMemoryCell<String> valueB = new GenericMemoryCell<String>("3");
        System.out.println("valueA (A): " + valueA.readA());
        System.out.println("valueA (B): " + valueA.readB());
        System.out.println("valueB (A): " + valueB.readA());
        System.out.println("valueB (B): " + valueB.readB());
    }

    public GenericMemoryCell(T storedValueA, T storedValueB) {
        this.storedValueA = storedValueA;
        this.storedValueB = storedValueB;
    }

    public GenericMemoryCell(T storedValueB) {
        this.storedValueB = storedValueB;
    }

    public void writeB(T storedValueB) {
        this.storedValueB = storedValueB;

    }

    public void writeA(T storedValueA) {
        this.storedValueA = storedValueA;

    }

    public T readA() {
        return storedValueA;
    }

    public T readB() {
        return storedValueB;
    }

    private T storedValueA, storedValueB;
}

GenericMemoryCell <t>类中的GenericMemoryCell不能应用于给定类型

2 个答案: