單利模式雙重鎖檢查優化

/**
 * DoubleCheckedLocking
 * 雙重鎖檢查優化，採用的是volatile來檢查
 * @author xiaoyi
 * @date 2020/5/24 14:57
 */
public class DoubleCheckedLocking {

	private volatile static DoubleCheckedLocking instance;

	public static DoubleCheckedLocking getInstance() {
		if (instance == null) {
			synchronized (DoubleCheckedLocking.class) {
				if (instance == null) {
					instance = new DoubleCheckedLocking();
				}
			}
		}
		return instance;
	}
}