一个特殊的双列集合：Properties

• Properties
  
  • 实现了Map接口
  • 可以与IO流结合

package bull1715.Properties;

import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;
import java.util.Set;

/* * Properties:表示了一个持久的属性值，属性列表中每个键及其对应值都是一个字符串 * * 构造方法： * Properties(); */
public class PropertiesDemo1 {
    public static void main(String[] args) {
        //创建属性列表对象
        Properties prop = new Properties();
        //添加映射关系
        prop.put("张三", "001");
        prop.put("李四", "002");
        prop.put("王五", "003");

        //遍历方式一,先获取key对象，再根据key对象获取value
        Set<Object> s = prop.keySet();
        for (Object object : s) {
            Object value = prop.get(object);
            System.out.println(object + "=" + value);
        }
        System.out.println("-------------------");
        //遍历方式二,获取整组对象
        Set<Map.Entry<Object, Object>> entrys = prop.entrySet();
        for (Entry<Object, Object> entry : entrys) {
            Object key = entry.getKey();
            Object value = entry.getValue();
            System.out.println(key + "=" + value);  
        }
    }
}

• Properties和IO流结合的功能：

package bull1715.Properties;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Properties;

/* * Properties和IO流结合的功能： * void load(Reader reader); * void list(PrintWriter list);只能写打印流 * void store(Writer writer,String comments);其中Sring comments是对文件数据的描述 */
public class PropertiesDemo2 {
    public static void main(String[] args) throws IOException {
        //写数据方式一
        method1();
        //读数据
        method2();
        //写数据方式二
        method3();
    }

    private static void method3() throws IOException {
        //创建属性列表对象
        Properties prop = new Properties();
        //创建输出流对象
        FileWriter fw = new FileWriter("PD2.txt");
        //添加映射对象
        prop.setProperty("张一", "0001");
        prop.setProperty("李二", "0002");
        prop.setProperty("王三", "0003");
        //void store(Writer writer,String comments);其中Sring comments是对文件数据的描述
        prop.store(fw, "PropertiesDemo2");
        //释放资源
        fw.close();
    }

    private static void method2() throws FileNotFoundException, IOException {
        //创建属性列表对象
        Properties prop = new Properties();
        //创建输入流对象
        FileReader fr = new FileReader("PD2.txt");

        prop.load(fr);
        //释放资源
        fr.close();
        System.out.println(prop);
    }

    private static void method1() throws FileNotFoundException {
        //创建属性列表对象
        Properties prop = new Properties();
        //创建打印流对象
        PrintWriter pw = new PrintWriter("PD2.txt");

        prop.setProperty("张三", "001");
        prop.setProperty("李四", "002");
        prop.setProperty("王五", "003");
        //void list(PrintWriter list);
        prop.list(pw);
        //释放资源
        pw.close();
    }
}