前面說了單例模式，這次說說單例模式的推廣——多例模式。

有上限多例模式
com.cleversoft.designpatterns.multiton.Die.java:
package?com.cleversoft.designpatterns.multiton;

import?java.util.Random;
import?java.util.Date;

public?class?Die?{
????private?static?Die?die1?=?new?Die();

????private?static?Die?die2?=?new?Die();

????private?Die()?{
????}

????public?static?Die?getInstance(int?whichOne)?{
????????if?(whichOne?==?1)?{
????????????return?die1;
????????}?else?{
????????????return?die2;
????????}
????}

????public?synchronized?int?dice()?{
????????Date?d?=?new?Date();

????????Random?r?=?new?Random(d.getTime());
????????int?value?=?r.nextInt();
????????value?=?Math.abs(value);

????????value?=?value?%?6;
????????value?+=?1;
????????System.out.println(value);
????????return?value;
????}

}

com.cleversoft.designpatterns.multiton.Main.java:
package?com.cleversoft.designpatterns.multiton;

public?class?Main?{
????private?static?Die?die1;

????private?static?Die?die2;

????public?static?void?main(String[]?args)?{
????????die1?=?Die.getInstance(1);
????????die2?=?Die.getInstance(2);

????????die1.dice();
????????die2.dice();
????}
}

無上限多例模式
比較合適的例子就是在應用程序中的“多語言支持”和序列鍵生成器。


參考資料：《Java與模式》

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