• interface definitions and abstract Classes

Multiple standards involved:

Note: Compatible hardware must obey both standards.

public class Text2File {
  private final PrintStream out;

  public Text2File(final String fileName)
     throws FileNotFoundException {
    out = new PrintStream(new File(fileName));}

  public void println(final String s) {
    out.println(s);}

  public void closeFile() {
    out.close();}
}

accessModifier interface interfaceName [throwsClause]?{
    [field]*
   [method]*
}

/**
 * Support auto-closing of resources
 */
public interface MyAutoCloseable {
  /**
   * close resource in question. Example: Terminate
   * a database connection or a file stream.
   */
  public void close();
}

/**
 * Flush pending values.
 */
public interface MyFlushable extends MyAutoCloseable {

  /**
   * Save pending i.e. buffered values.
   */
  public void flush();
}

public class Text2FileFlushable implements MyFlushable {
  private PrintStream out;
...
  /**
   * Flushing pending output to underlying file.
   */
  public void flush(){
    out.flush();
  }
  /**
   * Closing file thereby flushing buffer. Caution: Further calls
   * to {@link #println(String)} will fail!.
   */
  public void close() {
    out.close();
    out = null;
  }
}

• interface definitions and abstract Classes
  • ➟ Interfaces and sorting

interface Comparable<T> {
                ┌────┘  
                ▼
  int compareTo​(T o);

}

public class String implements Comparable <String ❶>, ... {
  ...                           ┌────────────┘          
  @Override                     ▼
  public int compareTo(final String ❷ other) {
     ...
    return ...;
  }
}

179. Understanding Arrays.sort()
180. Sorting Rectangle instances by width
181. Sorting Rectangle instances by width and height

Solution: Provide your own Comparator!

import java.util.Comparator;

public class SortCaseInsensitive implements Comparator<String> {
                              ┏━━━━━━━━━━━━━━┳━━━━━━━━━━━┛
  @Override                   ▼              ▼
  public int compare(final String a, final String b) {
    return a.toLowerCase().compareTo(b.toLowerCase());
  }
}

182. Adding flexibility in sorting rectangles
183. A nonsense generator
184. An interface based plotter
185. Various integer array algorithms
186. A command line version computing a sample's average and median
187. Adding line numbers to text files
188. A partial implementation of GNU UNIX wc