装饰器模式例子

Java IO中就是典型的装饰器

//InputStream提供的基本方法(Component)
public abstract class InputStream implements Closeable {

}
//默认目标实现类(ConcreteComponent)
public class FileInputStream extends InputStream {

}
/*装饰实现类（FilterInputStream）一定是继承或实现原始接口(InputStream)的，内部有包含一个原始接口的超类(其实就是某个默认目标实现类)*/
//Decorator
public class FilterInputStream extends InputStream {
    /**
     * The input stream to be filtered.
     */
    protected volatile InputStream in;

    protected FilterInputStream(InputStream in) {
        this.in = in;
    }
}
//具体装饰类(ConcreteDecorator)
public class BufferedInputStream extends FilterInputStream {

    public BufferedInputStream(InputStream in) {
        this(in, DEFAULT_BUFFER_SIZE);
    }
}
//具体装饰类(ConcreteDecorator)
public class DataInputStream extends FilterInputStream implements DataInput {

    public DataInputStream(InputStream in) {
        super(in);
    }
}