strapfontfactory.java

是内存受限系统设计的代码。

import java.awt.*;

class StrapFont {
    // Functions to return fonts reliably
        
    static int countdownToDoom = 0;

    public static void simulateMemoryFailureNext( int n ) {
    // Simulates memory allocation failure for all allocs starting with the
    // n-th allocation
    // after now (n=1 for first).  Resets previous calls to this func.
    // n==0 resets to normal

        countdownToDoom = n;
    }

    static Font myDefaultFont =  new Font("Dialog",Font.PLAIN,12);

    public static Font defaultFont() {
    // Returns the default font object.
        return myDefaultFont;
    }

    public static Font font( String fontDescription ) { 
        Font f;
        try {
            f = privateGetFont(fontDescription); 
        }
        catch (BadFontException e) {
            return defaultFont();
        } catch (OutOfMemoryError e) {
            return defaultFont();
        }
        return f;
    };
    
    protected static Font privateGetFont(String fontDescription ) 
    // Returns a font. 
        throws BadFontException
    {
        if ("BadFont".equals(fontDescription)) {
            throw new BadFontException();
        }
        if (countdownToDoom > 0) {
            if (countdownToDoom == 1)
                throw new OutOfMemoryError();
            countdownToDoom--;
        };
        return new Font(fontDescription,Font.PLAIN,12);
    }
};

class BadFontException extends Exception { };

class PartialFailureTest {
    // Test class for StrapFont:
        
    private static final String GoodFontDescription = "Dialog";
        
    public static void assert( boolean b, String reason ) {
        if (!b) {
            System.out.println("Assertion failed: " + reason ); 
            try {System.in.read();} catch (Exception e) {};
            System.exit(1);
        }
    }
                
    public static void main( String[] args )
    {
        //        StrapFont factory = new StrapFont();
        // Tests:

        try {
            // Get a font normally.
            Font newFont = StrapFont.font( GoodFontDescription );
            System.out.print(".");
            assert( newFont != null, "Courier font null" );
            assert( newFont != StrapFont.defaultFont(),
                    "Courier font same as system" );
            assert( newFont.getName().equals(GoodFontDescription), "wrong font name!" );
            // TODO Check semantics of Font class ...!
                
            // Kill this instance (Some implementations might use weak collections
            // to cache it):
            newFont = null;
            System.gc();
            System.out.print(".");              
            // Get a font that doesn't exist
            newFont = StrapFont.font( "BadFont" );
            assert( newFont != null, "Bad font returns null" );
            assert( newFont.equals(StrapFont.defaultFont()),
                    "Bad font not same as system" );
            System.out.print(".");
            // Get a font with memory failure

            StrapFont.simulateMemoryFailureNext(20);

            for (int i=1; i < 25; i++) {
                System.out.print(".");
                assert( i < 25, "Mem failure testing problem" );
                newFont = StrapFont.font( GoodFontDescription );
                assert( newFont != null, "Mem failure returns null" );
                assert( newFont.equals(StrapFont.defaultFont()) || i < 20,  
                        "Mem failure doesn't return system font" );
            }
            assert( newFont.getName().equals(GoodFontDescription) , "Wrong font name" );
        
        }       catch (Exception e) {
            assert( false, "font function threw exception" );
        } 
        System.out.println("done");
        return;
    }
}