为什么Properties.list（PrintWriter out）不打印任何内容？

Question

I'm new to Java and is trying to learn the class Properties. I have came up with the code below. I wanted to print the "keys" and "values" stored in Properties variable p2 using different methods. However, the code

PrintWriter pw1 = new PrintWriter(System.out);
p2.list(pw1);

Doesn't seem to be printing out anything. Why is this happening? Could someone please help me out? Thanks in advance for any help!

Properties p1 = new Properties();

try (OutputStream os1 = new FileOutputStream("whateverAmericaFile2.txt")){
    p1.setProperty("1", "one");
    p1.setProperty("2", "two");
    p1.setProperty("3", "three");
    p1.store(os1, "comment");
} catch(IOException e){
    e.printStackTrace();
}

Properties p2 = new Properties();
try (InputStream is1 = new FileInputStream("whateverAmericaFile2.txt")){
    p2.load(is1);
    System.out.println(p2.getProperty("2"));
} catch (IOException e){
    e.printStackTrace();
}

System.out.println("before PrintWriter");

PrintWriter pw1 = new PrintWriter(System.out);
p2.list(pw1);


System.out.println("After PrintWriter, before Enumeration ");

Enumeration<Object> eo1 = p2.elements();
while (eo1.hasMoreElements()){
    System.out.println(eo1.nextElement());
}

System.out.println("after Enumeration");

}

Answer 1

您必须在p2.list(pw1) pw1.flush()之后调用pw1.flush()才能将缓存的文本写入控制台。