实现相同接口的接口内的内部类,我们通过这个实现了什么？

Question

我的问题:

我正在查看TextWatcher的源代码,我没有在这里得到这个概念.扩展到NoCopySpan有什么意义？

TextWatcher.java:

public interface TextWatcher extends NoCopySpan {
     public void beforeTextChanged(CharSequence s, int start, int count, int after);
     public void onTextChanged(CharSequence s, int start, int before, int count);
     public void afterTextChanged(Editable s);
}

NoCopySpan.java:

package android.text;

/**
 * This interface should be added to a span object that should not be copied into a new Spanned when performing a slice or copy operation on the original Spanned it was placed in.
 */
public interface NoCopySpan {
    /**
     * Convenience equivalent for when you would just want a new Object() for
     * a span but want it to be no-copy.  Use this instead.
     */
    public class Concrete implements NoCopySpan {}
}

Answer 1

NoCopySpan只是一个标记界面.根据javadoc,它用于修改Spanned对象的复制例程的行为(它依赖于组件的类型).例如,android.text.SpannableStringBuilder使用此类继承信息来跳过跨构造时的复制.

这种方法有一些缺点,但仍然很常见.Concrete类存在的原因是提供构造接口的on-op虚拟(或默认)实现的便捷方式NoCopySpan.