java - 在 Java 中使用类的接口(interface)

Question

我对在 Java 中使用接口(interface)有点困惑。我已经为 Bag java 类创建了一个接口(interface)。看来我实现该接口(interface)的唯一方法是在 Bag 类 header 中显式声明该类是抽象的。如果我这样做，那么我将无法创建另一个类，比如说一个使用 bag 类的 PiggyBank java 类。所以这让我对应该如何去做感到有些困惑。是否可以定义一个扩展 Bag 类的 PiggyBank 类？我还没有完成当前的 Bag 类，因为我不确定如何定义某些方法。然后我意识到，由于该类现在是抽象的，我将无法从测试类创建该类的新实例。

package bagimplementation;
/**
 An interface that the describes the operations of a bag of objects.
 @author Jeff nicholas
 * @param <T> The type of item being bagged
 */
public interface BagInterface <T> {
    /**Gets the current number of entries in this bag.
       @return the integer number of entries currently in the bag*/
    int getCurrentSize();

    /**Sees whether this bag is full.
       @return true if the bag is full, or false if not */
    boolean isFull();

    /**Sees whether this bag is empty.
       @return true if the bag is empty, or false if not */
    boolean isEmpty();

    /**Adds a new entry to this bag.
       @param newEntry the object to be added as a new entry.
       @return true if the addition is successful, or false if not */
    boolean add(T newEntry);

    /**Removes one unspecified entry from this bag, if possible.
       @return either the removed entry, if the removal was successful, or null*/
    T remove();

    /**Removes one occurrence of a given entry from this bag, if possible
       @param anEntry the entry the be removed.
       @return true if the removal was successful, or false if not */
    boolean remove(T anEntry);

    /**Removes all entries from this bag. */
    void clear();

    /**Counts the number of times a given entry appears in this bag.
       @param anEntry the entry to be counted.
       @return the number of times anEntry appears in the bag */
    int getFrequencyOf(T anEntry);

    /**Tests whether this bag contains a given entry.
     * @param anEntry the entry to locate
     * @return true if the bag contains anEntry, or false otherwise */
    boolean contaions(T anEntry);

    /**Creates an array of all entries that are in this bag.
     * @return a newly allocated array of all the entries in the bag*/
    T[] toArray();
}//end BagInterface

/**Bag class is not finished at this time */
package bagimplementation;
import java.util.*;
/**
 *
 * @author admin
 */
public abstract class Bag implements BagInterface<Bag>{

    private int size;
    private boolean full;
    private boolean empty;
    private int currentSize;

    public void setSize(int aSize){
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Enter a size for the bag.....");
        aSize = keyboard.nextInt();
        size = aSize;
    }//end setSize


    public int getCurrentSize(){
    return currentSize;
    }   


}

Answer 1

除非您将该类声明为抽象类，否则您必须实现该接口(interface)中的所有方法。如果您不知道如何实现某些方法，只需添加一些像这样的临时 stub 实现，然后当您弄清楚时，将其替换为真正的实现:

public boolean isEmpty() {
    // TODO: implement functionality
    return false;
}

当您选择实现接口(interface)时，某些 IDE 还会为您生成这些 stub 方法。