// Example 119 from page 91

//

import java.util.*;

/*

Since it is illegal to create an array by new T[SIZE] in class Log<T>,

we must pass a suitable array to the constructor.

Similarly, method getAll() could not return an array of type T[],

because it is not allowed to create such an array. Also, it cannot

use res.toArray(log) to create an array with the right element type,

as that would overwrite the log array...

*/

class Log<T> {

private final int size;

private static int instanceCount = 0;

private int count = 0;

private T[] log;

public Log(T[] log) {

this.log = log;

this.size = log.length;

instanceCount++;

}

public static int getInstanceCount() { return instanceCount; }

public void add(T msg) { log[count++ % size] = msg; }

public int getCount() { return count; }

public T getLast() {

// Return the last log entry, or null if nothing logged yet

return count==0 ? null : log[(count-1)%size];

}

public void setLast(T value) {

// Update the last log entry, or create one if nothing logged yet

if (count==0)

log[count++] = value;

else

log[(count-1)%size] = value;

}

public ArrayList<T> getAll() {

ArrayList<T> res = new ArrayList<T>();

int stop = Math.min(count, size);

for (int i=0; i<stop; i++)

res.add(log[(count-stop+i) % size]);

return res;

}

}

class Example119 {

public static void main(String[] args) {

// Log<String> log1 = new Log<String>(new String[5]);

Log<String> log1 = new Log<>(new String[5]); // Shorthand for the above

log1.add("Reboot");

log1.add("Coffee");

// Log<Date> log2 = new Log<Date>(new Date[5]); // Shorthand for the above

Log<Date> log2 = new Log<>(new Date[5]);

log2.add(new Date()); // now

log2.add(new Date(new Date().getTime() + 60*60*1000)); // now + 1 hour

ArrayList<Date> dts = log2.getAll();

// Printing both logs:

for (String s : log1.getAll())

System.out.print(s + " ");

System.out.println();

for (Date dt : dts)

System.out.print(dt + " ");

System.out.println();

}

}