Singleton,了解一下

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原创最新推荐文章于 2026-07-02 09:54:37 发布 179 阅读 AI 写同款· GEO 优化 ›

ArcGIS基础：CAD数据转换为GIS数据（符号化显示、数据转换、线转面、空间连接） 1、符号化显示： CAD数据加载进来有很多列表，包含了点【point】、线【polyline】、面【polygon】、标注数据【Annotation】等数据，本次实验我们需要用到的是面数据，也就是.dwgPolygong格式的数据。如下图所示：把数据加载进来，然后在2处打开属性表，查看CAD数据的属性表，打开后可以发现【layer】图层表示就是地块的用地性质，它就是符号化显示的依据。我们在数据上右键【属性】，打开图层属性，找到【符号系统】，选择类别中的【唯一值】，然后在【值字段】下拉选择【layer】，阅读详情

package suanfa;

import java.util.concurrent.locks.ReentrantLock;

public class MySingleton {
    static class S1 {
        private static S1 instance;
        private S1() {
        }


        public static S1 getInstance() {
            if (instance == null) {
                instance = new S1();
            }
            return instance;
        }
    }

    static class S2 {
        private static S2 instance;
        public S2() {
        }
        public static synchronized S2 getInstance() {
            if (instance == null) {
                instance = new S2();

            }
            return instance;
        }
    }


    static class S3 {
        private static S3 instance;
        private static byte[] lock  = new byte[0];
        private S3() {
        }

        public static S3 getInstance() {
            if (instance == null) {
                synchronized (lock) {
                    if (instance == null) {
                        instance = new S3();
                    }

                }
            }
            return instance;
        }
    }


    static class S4 {
        private static S4 instance; 
        private static ReentrantLock lock = new ReentrantLock();
        private S4() {
        }

        public static S4 getInstance() {
            if (instance == null) {
                lock.lock();
                if (instance==null) {
                    instance = new S4();
                }
                lock.unlock();
            }
            return instance;
        }
    }


}