java - 字符串日志混淆接口(interface)

Question

我正在阅读《使用 Java 的面向对象的数据结构》一书，正在读第 2 章。我决定尝试一下他们在那里的练习之一，但代码似乎对我不起作用，尽管它们是直接的从书中。有人能澄清一下吗？

package chapter2;

public interface StringLogInterface
{
    void insert(String element);
    boolean isFull();
    int size();
    boolean contains(String element);
    void clear();
    String getName();
    String toString();
}

该项目使用三个文件，我在下面发布其余两个文件。

package chapter2;

public class ArrayStringLog
{
  protected String name;              
  protected String[] log;             
  protected int lastIndex = -1;       

  public ArrayStringLog(String name, int maxSize)
  {
    log = new String[maxSize];
    this.name = name;
  }

  public ArrayStringLog(String name) 
  {
    log = new String[100];
    this.name = name;
  }

  public void insert(String element)
  {      
    lastIndex++;
    log[lastIndex] = element;
  }

  public boolean isFull()
  {              
    if (lastIndex == (log.length - 1)) 
      return true;
    else
      return false;
  }

  public int size()
  {
    return (lastIndex + 1);
  }

  public boolean contains(String element)
  {                 
    int location = 0;
    while (location <= lastIndex) 
    {
      if (element.equalsIgnoreCase(log[location]))  // if they match
        return true;
      else
        location++;
    }
   return false;
  }

  public void clear()
  {                  
    for (int i = 0; i <= lastIndex; i++)
      log[i] = null;
    lastIndex = -1;
  }

  public String getName()
  {
    return name;
  }

  public String toString()
  {
    String logString = "Log: " + name + "\n\n";

    for (int i = 0; i <= lastIndex; i++)
      logString = logString + (i+1) + ". " + log[i] + "\n";

    return logString;
  }
}

最后一部分:

package chapter2;

public class UseStringLog
{
    public static void main(String[] args)
    { 
    StringLogInterface sample;
    sample = new ArrayStringLog("Example Use");
    sample.insert("Elvis");
    sample.insert("King Louis XII");
    sample.insert("Captain Kirk");
    System.out.println(sample);
    System.out.println("The size of the log is " + sample.size());
    System.out.println("Elvis is in the log: " + sample.contains("Elvis"));
    System.out.println("Santa is in the log: " + sample.contains("Santa"));
    }
}

最后一部分让我感到困惑。已上线，

sample = new ArrayStringLog("Example Use");

NetBeans 说“无法比较的类型，必需:StringLogInterface，找到:ArrayStringLog。

它们都构建成功，但是最后一个带有三个 println 语句的文件不应该打印出一些东西吗？

Answer 1

使ArrayStringLog实现StringLogInterface。

public class ArrayStringLog implements StringLogInterface {
  // ...
}

只有这样才有可能:

StringLogInterface sample;
sample = new ArrayStringLog("Example Use");