utils.java

java高级使用教程 全书一共分六章

		    String t = strings[i];
		    strings[i] = strings[j];
		    strings[j] = t;
		    }
		}
	    }
	}
    
    /// Locates a String in an array of Strings.
    // Returns -1 if the String is not found.
    public static int indexOfString( String[] strings, String string )
	{
	for ( int i = 0; i < strings.length; ++i )
	    if ( string.equals( strings[i] ) )
		return i;
	return -1;
	}

    /// Locates a String in an array of Strings, ignoring case.
    // Returns -1 if the String is not found.
    public static int indexOfStringIgnoreCase( String[] strings, String string )
	{
	for ( int i = 0; i < strings.length; ++i )
	    if ( string.equalsIgnoreCase( strings[i] ) )
		return i;
	return -1;
	}
    
    /// Compares two arrays of Strings for equality.
    public static boolean equalsStrings( String[] strings1, String[] strings2 )
	{
	if ( strings1.length != strings2.length )
	    return false;
	for ( int i = 0; i < strings1.length; ++i )
	    if ( ! strings1[i].equals( strings2[i] ) )
		return false;
	return true;
	}


    /// Returns the number a raised to the power of b.  Long version
    // of Math.pow().  Throws ArithmeticException if b is negative.
    public static long pow( long a, long b ) throws ArithmeticException
	{
	if ( b < 0 )
	    throw new ArithmeticException();
	long r = 1;
	while ( b != 0 )
	    {
	    if ( odd( b ) )
		r *= a;
	    b >>>= 1;
	    a *= a;
	    }
	return r;
	}


    /// Parse an integer, returning a default value on errors.
    public static int parseInt( String str, int def )
	{
	try
	    {
	    return Integer.parseInt( str );
	    }
	catch ( Exception e )
	    {
	    return def;
	    }
	}

    /// Parse a long, returning a default value on errors.
    public static long parseLong( String str, long def )
	{
	try
	    {
	    return Long.parseLong( str );
	    }
	catch ( Exception e )
	    {
	    return def;
	    }
	}


    /// An array-to-String routine.  Handles arrays of arbitrary
    // type, including nested arrays.  Sample output:
    // <BLOCKQUOTE><CODE><PRE>
    // byte[]:    { (byte)0, (byte)1, (byte)2 }
    // char[]:    { '0', '1', '2' }
    // short[]:   { (short)0, (short)1, (short)2 }
    // int[]:     { 0, 1, 2 }
    // long[]:    { 0L, 1L, 2L }
    // float[]:   { 0F, 1F, 2F }
    // double[]:  { 0D, 1D, 2D }
    // String[]:  { "0", "1", "2" }
    // int[][]:   { { 0, 1, 2 }, { 3, 4, 5 } }
    // </PRE></CODE></BLOCKQUOTE>
    public static String arrayToString( Object o )
	{
	if ( o == null )
	    return "null";
	String cl = o.getClass().getName();
	if ( ! cl.startsWith( "[" ) )
	    // It's not an array; just call its toString method.
	    return o.toString();
	StringBuffer sb = new StringBuffer( "{ " );
	if ( o instanceof byte[] )
	    {
	    byte[] ba = (byte[]) o;
	    for ( int i = 0; i < ba.length; ++i )
		{
		if ( i > 0 ) sb.append( ", " );
		sb.append( "(byte)" );
		sb.append( ba[i] );
		}
	    }
	else if ( o instanceof char[] )
	    {
	    char[] ca = (char[]) o;
	    for ( int i = 0; i < ca.length; ++i )
		{
		if ( i > 0 ) sb.append( ", " );
		sb.append( "'" );
		sb.append( ca[i] );
		sb.append( "'" );
		}
	    }
	else if ( o instanceof short[] )
	    {
	    short[] sa = (short[]) o;
	    for ( int i = 0; i < sa.length; ++i )
		{
		if ( i > 0 ) sb.append( ", " );
		sb.append( "(short)" );
		sb.append( sa[i] );
		}
	    }
	else if ( o instanceof int[] )
	    {
	    int[] ia = (int[]) o;
	    for ( int i = 0; i < ia.length; ++i )
		{
		if ( i > 0 ) sb.append( ", " );
		sb.append( ia[i] );
		}
	    }
	else if ( o instanceof long[] )
	    {
	    long[] la = (long[]) o;
	    for ( int i = 0; i < la.length; ++i )
		{
		if ( i > 0 ) sb.append( ", " );
		sb.append( la[i] );
		sb.append( "L" );
		}
	    }
	else if ( o instanceof float[] )
	    {
	    float[] fa = (float[]) o;
	    for ( int i = 0; i < fa.length; ++i )
		{
		if ( i > 0 ) sb.append( ", " );
		sb.append( fa[i] );
		sb.append( "F" );
		}
	    }
	else if ( o instanceof double[] )
	    {
	    double[] da = (double[]) o;
	    for ( int i = 0; i < da.length; ++i )
		{
		if ( i > 0 ) sb.append( ", " );
		sb.append( da[i] );
		sb.append( "D" );
		}
	    }
	else if ( o instanceof String )
	    {
	    // Special-case Strings so we can surround them with quotes.
	    String[] sa = (String[]) o;
	    for ( int i = 0; i < sa.length; ++i )
		{
		if ( i > 0 ) sb.append( ", " );
		sb.append( "\"" );
		sb.append( sa[i] );
		sb.append( "\"" );
		}
	    }
	else if ( cl.startsWith( "[L" ) )
	    {
	    // Some random class.
	    Object[] oa = (Object[]) o;
	    for ( int i = 0; i < oa.length; ++i )
		{
		if ( i > 0 ) sb.append( ", " );
		sb.append( oa[i] );
		}
	    }
	else if ( cl.startsWith( "[[" ) )
	    {
	    // Nested arrays.
	    Object[] aa = (Object[]) o;
	    for ( int i = 0; i < aa.length; ++i )
		{
		if ( i > 0 ) sb.append( ", " );
		sb.append( arrayToString( aa[i] ) );
		}
	    }
	else
	    sb.append( "(unknown array type)" );
	sb.append( " }" );
	return sb.toString();
	}


    /// Check if an object extends a given class or one of its superclasses.
    // An instanceof that works on Class objects at runtime, instead
    // of type descriptors at compile time.
    public static boolean instanceOf( Object o, Class cl )
	{
	// Null check.
	if ( o == null || cl == null )
	    return false;
	Class ocl = o.getClass();
	// Check if they are the same class.
	if ( ocl.equals( cl ) )
	    return true;
	// If the class is not itself an interface, then check its interfaces.
	if ( ! cl.isInterface() )
	    {
	    Class ifs[] = cl.getInterfaces();
	    for ( int i = 0; i < ifs.length; ++i )
		if ( instanceOf( o, ifs[i] ) )
		    return true;
	    }
	// And check supeclasses.
	Class scl = cl.getSuperclass();
	if ( scl != null )
	    if ( instanceOf( o, scl ) )
		return true;
	// Guess not.
	return false;
	}


    /// Test is a number is even.
    public static boolean even( long n )
	{
	return ( n & 1 ) == 0;
	}

    /// Test is a number is odd.
    public static boolean odd( long n )
	{
	return ( n & 1 ) != 0;
	}


    /// Count the number of 1-bits in a byte.
    public static int countOnes( byte n )
	{
	return countOnes( n & 0xffL );
	}

    /// Count the number of 1-bits in an int.
    public static int countOnes( int n )
	{
	return countOnes( n & 0xffffffffL );
	}

    /// Count the number of 1-bits in a long.
    public static int countOnes( long n )
	{
	// There are faster ways to do this, all the way up to looking
	// up bytes in a 256-element table.  But this is not too bad.
	int count = 0;
	while ( n != 0 )
	    {
	    if ( odd( n ) )
		++count;
	    n >>>= 1;
	    }
	return count;
	}


    /// A fixed version of java.io.InputStream.read(byte[], int, int).  The
    // standard version catches and ignores IOExceptions from below.
    // This version sends them on to the caller.
    public static int read( InputStream in, byte[] b, int off, int len ) throws IOException
        {
        if ( len <= 0 )
            return 0;
        int c = in.read();
        if ( c == -1 )
            return -1;
        if ( b != null )
            b[off] = (byte) c;
        int i;
        for ( i = 1; i < len ; ++i )
            {
            c = in.read();
            if ( c == -1 )
                break;
            if ( b != null )
                b[off + i] = (byte) c;
            }
        return i;
        }

    /// A version of read that reads the entire requested block, instead
    // of sometimes terminating early.
    // @return -1 on EOF, otherwise len
    public static int readFully( InputStream in, byte[] b, int off, int len ) throws IOException
        {
	int l, r;
	for ( l = 0; l < len; )
	    {
	    r = read( in, b, l, len - l );
	    if ( r == -1 )
		return -1;
	    l += r;
	    }
	return len;
	}


    /// Make a URL with no ref part and no query string.  Also, if it's
    // a directory then make sure there's a trailing slash.
    public static URL plainUrl( URL context, String urlStr ) throws MalformedURLException
	{
	URL url = new URL( context, urlStr );
	String fileStr = url.getFile();
	int i = fileStr.indexOf( '?' );
	if ( i != -1 )
	    fileStr = fileStr.substring( 0, i );
	url = new URL(
	    url.getProtocol(), url.getHost(), url.getPort(), fileStr );
	if ( ( ! fileStr.endsWith( "/" ) ) &&
	     urlStrIsDir( url.toExternalForm() ) )
	    {
	    fileStr = fileStr + "/";
	    url = new URL(
		url.getProtocol(), url.getHost(), url.getPort(), fileStr );
	    }
	return url;
	}

    /// Make a URL with no ref part and no query string.  Also, if it's
    // a directory then make sure there's a trailing slash.
    public static URL plainUrl( String urlStr ) throws MalformedURLException