我們分析HttpServlet源代碼就會發明,其供給了一個public的構造函數,此外也不能找到static的getInstance方法。
import java.awt.Font;
import java.util.HashMap;
import java.util.Map;

interface FontProvider {
public Font getFont(String name);
}

class DefaultFontProvider implements FontProvider {
public Font getFont(String name) {
return new Font(name, Font.PLAIN, 12);
}
}

class BufferedFontProvider implements FontProvider {

private FontProvider fontProvider;
private Map<String, Font> fontCache = new HashMap();

public BufferedFontProvider(FontProvider fontProvider) {
this.fontProvider = fontProvider;
}