Java基础知识学习2
1.文件的输入输出。scanner in = new scaner（new File("myfile.txt")）;当如果是绝对地址时，每个\前都要加一个\. 写入文件 PrintWriter out = new PrintWriter("myfile.txt")


Scanner in = new Scanner(FileRead("path"));
while(in.hasnext)
{
System.out.print(in.nextLine());
}

2.文件写入。PrintWriter使用后要close。要不然写的数据不会存进去。
PrintWriter pw = new PrintWriter("c:\\test.txt");
pw.write("marry wyp!happiness");
pw.close();
Scanner in = new Scanner(new FileReader("c:\\test.txt"));
while(in.hasNext())
{
System.out.println(in.nextLine());
}

3.文件创建。
File f = new FIle("PATH")
f.createNewFile();
4.循环控制。gob bless me
System.out.print("Do you love me? wyp(yes or no)");
Scanner in = new Scanner(System.in);
String str = in.next();
while(!str.equalsIgnoreCase("yes"))
{
System.out.println("please answer again");
str = in.next();
}
if(str.equalsIgnoreCase("yes"))
{
System.out.println("right,marry me!");
}

5.switch中只能使用枚举类型或者整型。不能用字符串等！

6. 数组。for each 遍历数组拷贝。 Array.copyOf(array,length); 或者System.arrayCopy(from, fromIdex, to, toIndex, count);

7.IO流操作！
public static void main(String[] args) {
try {
// TODO code application logic here
FileInputStream fis = new FileInputStream("c:\\test.txt");
RandomAccessFile raf = new RandomAccessFile("e:\\forever.txt", "r");
int flag = 0;
try {
while((flag = raf.read())!= -1 )
{
System.out.print((char)flag);
}
} catch (IOException ex) {
Logger.getLogger(FileIO.class.getName()).log(Level.SEVERE, null, ex);
}
// FileOutputStream fos = new FileOutputStream("e:\\forever.txt");
// System.out.println("file content is:");
int b;
try {
while((b = fis.read()) != -1)
{
// fos.write(b);
System.out.print((char) b );
}
// fos.close();
} catch (IOException ex) {
Logger.getLogger(FileIO.class.getName()).log(Level.SEVERE, null, ex);
}
} catch (FileNotFoundException ex) {
Logger.getLogger(FileIO.class.getName()).log(Level.SEVERE, null, ex);
}


}

8. 未初始化的对象不是对象。如 Date() birthday ; 如果调用birthday.toString();会报错！必须初始化之后才能使用。

9.当一个方法不需要访问对象状态。其所需的参数都是通过显示参数提供。或者一个方法需要访问类的静态域时。将该方法声明为静态方法。