JavaIO流

标签：fs parent JavaIO pathname File child path

Java File类的功能非常强大，利用java基本上可以对文件进行所有操作。

我们看看源码

   /**
     * Internal constructor for already-normalized pathname strings.
     */
  private File(String pathname, int prefixLength) {
        this.path = pathname;
        this.prefixLength = prefixLength;
    }

    /**
     * Internal constructor for already-normalized pathname strings.
     * The parameter order is used to disambiguate this method from the
     * public(File, String) constructor.
     */
    private File(String child, File parent) {
        assert parent.path != null;
        assert (!parent.path.equals(""));
        this.path = fs.resolve(parent.path, child);
        this.prefixLength = parent.prefixLength;
    }

    /**
     * Creates a new <code>File</code> instance by converting the given
     * pathname string into an abstract pathname.  If the given string is
     * the empty string, then the result is the empty abstract pathname.
     *
     * @param   pathname  A pathname string
     * @throws  NullPointerException
     *          If the <code>pathname</code> argument is <code>null</code>
     */
    public File(String pathname) {
        if (pathname == null) {
            throw new NullPointerException();
        }
        this.path = fs.normalize(pathname);
        this.prefixLength = fs.prefixLength(this.path);
    }

 
     /**
     * @param   parent  The parent pathname string
     * @param   child   The child pathname string
     * @throws  NullPointerException
     *          If <code>child</code> is <code>null</code>
     */
    public File(String parent, String child) {
        if (child == null) {
            throw new NullPointerException();
        }
        if (parent != null && !parent.isEmpty()) {
            this.path = fs.resolve(fs.normalize(parent),
                                   fs.normalize(child));
        } else {
            this.path = fs.normalize(child);
        }
        this.prefixLength = fs.prefixLength(this.path);
    }

    /**
     * @param   parent  The parent abstract pathname
     * @param   child   The child pathname string
     * @throws  NullPointerException
     *          If <code>child</code> is <code>null</code>
     */
    public File(File parent, String child) {
        if (child == null) {
            throw new NullPointerException();
        }
        if (parent != null) {
            if (parent.path.equals("")) {
                this.path = fs.resolve(fs.getDefaultParent(),
                                       fs.normalize(child));
            } else {
                this.path = fs.resolve(parent.path,
                                       fs.normalize(child));
            }
        } else {
            this.path = fs.normalize(child);
        }
        this.prefixLength = fs.prefixLength(this.path);
    }

    /**
     * @param  uri
     *         An absolute, hierarchical URI with a scheme equal to
     *         <tt>"file"</tt>, a non-empty path component, and undefined
     *         authority, query, and fragment components
     *
     * @throws  NullPointerException
     *          If <tt>uri</tt> is <tt>null</tt>
     *
     * @throws  IllegalArgumentException
     *          If the preconditions on the parameter do not hold
     */
    public File(URI uri) {

        // Check our many preconditions
        if (!uri.isAbsolute())
            throw new IllegalArgumentException("URI is not absolute");
        if (uri.isOpaque())
            throw new IllegalArgumentException("URI is not hierarchical");
        String scheme = uri.getScheme();
        if ((scheme == null) || !scheme.equalsIgnoreCase("file"))
            throw new IllegalArgumentException("URI scheme is not \"file\"");
        if (uri.getAuthority() != null)
            throw new IllegalArgumentException("URI has an authority component");
        if (uri.getFragment() != null)
            throw new IllegalArgumentException("URI has a fragment component");
        if (uri.getQuery() != null)
            throw new IllegalArgumentException("URI has a query component");
        String p = uri.getPath();
        if (p.equals(""))
            throw new IllegalArgumentException("URI path component is empty");

        // Okay, now initialize
        p = fs.fromURIPath(p);
        if (File.separatorChar != '/')
            p = p.replace('/', File.separatorChar);
        this.path = fs.normalize(p);
        this.prefixLength = fs.prefixLength(this.path);
    }

从源码可以看出File类的构造函数有6个，精简如下

public File(String pathname)  //文件的绝对路径
public File(URI uri)  //文件的URI地址

public File(String parent, String child)  //指定父文件绝对路径、子文件绝对路径
public File(File parent, String child)  //指定父文件、子文件相对路径


//下面这两个是File类中私有的构造函数，外面不能调用
private File(String child, File parent)  
private File(String pathname, int prefixLength) 

现在就看的比较清楚了，6个构造函数，可以分为2类。4个公共构造函数，2个私有构造函数。

构造函数1：

//电脑d盘中的 D:\ioTest\demo01.txt 的路径
String filePath1 = "D:\ioTest\demo01.txt" ;
File file = new File( filePath1 ) ;

标签：fs,parent,JavaIO,pathname,File,child,path
From： https://www.cnblogs.com/mingcodeing/p/16614601.html