位掩码（BitMask）
位运算在实际开发中用得很少，主要原因还是它对于不熟悉的人不好读不好懂不好计算，如果不经常实践会生疏。但它的优点自然是计算快，代码更少。在某些地方它的优势会更加明显比如如下代码（http://xxgblog.com/2013/09/15/java-bitmask/）：
public class NewPermission {
// 是否允许查询，二进制第1位，0表示否，1表示是
public static final int ALLOW_SELECT = 1 << 0; // 0001
// 是否允许新增，二进制第2位，0表示否，1表示是
public static final int ALLOW_INSERT = 1 << 1; // 0010
// 是否允许修改，二进制第3位，0表示否，1表示是
public static final int ALLOW_UPDATE = 1 << 2; // 0100
// 是否允许删除，二进制第4位，0表示否，1表示是
public static final int ALLOW_DELETE = 1 << 3; // 1000
// 存储目前的权限状态
private int flag;
/**
* 重新设置权限
*/
public void setPermission(int permission) {
flag = permission;
}
/**
* 添加一项或多项权限
*/
public void enable(int permission) {
flag |= permission;
}
/**
* 删除一项或多项权限
*/
public void disable(int permission) {
flag &= ~permission;
}
/**
* 是否拥某些权限
*/
public boolean isAllow(int permission) {
return (flag & permission) == permission;
}
/**
* 是否禁用了某些权限
*/
public boolean isNotAllow(int permission) {
return (flag & permission) == 0;
}
/**
* 是否仅仅拥有某些权限
*/
public boolean isOnlyAllow(int permission) {
return flag == permission;
}
}在业务上，权限可以有多个，通过普通方式实现上面的业务功能也不会太麻烦。但上面这种取巧的方式在android的源码中是不少的，可以说是随处可见，比如EditText的InputType：
/*
* Copyright (C) 2008 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.text;
import android.text.TextUtils;
/**
* Bit definitions for an integer defining the basic content type of text
* held in an {@link Editable} object. Supported classes may be combined
* with variations and flags to indicate desired behaviors.
*
* Examples
*
*
* - A password field with with the password visible to the user:
*
- inputType = TYPE_CLASS_TEXT |
* TYPE_TEXT_VARIATION_VISIBLE_PASSWORD
*
*
- A multi-line postal address with automatic capitalization:
*
- inputType = TYPE_CLASS_TEXT |
* TYPE_TEXT_VARIATION_POSTAL_ADDRESS |
* TYPE_TEXT_FLAG_MULTI_LINE
*
*
- A time field:
*
- inputType = TYPE_CLASS_DATETIME |
* TYPE_DATETIME_VARIATION_TIME
*
*/
public interface InputType {
/**
* Mask of bits that determine the overall class
* of text being given. Currently supported classes are:
* {@link #TYPE_CLASS_TEXT}, {@link #TYPE_CLASS_NUMBER},
* {@link #TYPE_CLASS_PHONE}, {@link #TYPE_CLASS_DATETIME}.
* IME authors: If the class is not one you
* understand, assume {@link #TYPE_CLASS_TEXT} with NO variation
* or flags.
*/
public static final int TYPE_MASK_CLASS = 0x0000000f;
/**
* Mask of bits that determine the variation of
* the base content class.
*/
public static final int TYPE_MASK_VARIATION = 0x00000ff0;
/**
* Mask of bits that provide addition bit flags
* of options.
*/
public static final int TYPE_MASK_FLAGS = 0x00fff000;
/**
* Special content type for when no explicit type has been specified.
* This should be interpreted to mean that the target input connection
* is not rich, it can not process and show things like candidate text nor
* retrieve the current text, so the input method will need to run in a
* limited "generate key events" mode, if it supports it. Note that some
* input methods may not support it, for example a voice-based input
* method will likely not be able to generate key events even if this
* flag is set.
*/
public static final int TYPE_NULL = 0x00000000;
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
/**
* Class for normal text. This class supports the following flags (only
* one of which should be set):
* {@link #TYPE_TEXT_FLAG_CAP_CHARACTERS},
* {@link #TYPE_TEXT_FLAG_CAP_WORDS}, and.
* {@link #TYPE_TEXT_FLAG_CAP_SENTENCES}. It also supports the
* following variations:
* {@link #TYPE_TEXT_VARIATION_NORMAL}, and
* {@link #TYPE_TEXT_VARIATION_URI}. If you do not recognize the
* variation, normal should be assumed.
*/
public static final int TYPE_CLASS_TEXT = 0x00000001;
/**
* Flag for {@link #TYPE_CLASS_TEXT}: capitalize all characters. Overrides
* {@link #TYPE_TEXT_FLAG_CAP_WORDS} and
* {@link #TYPE_TEXT_FLAG_CAP_SENTENCES}. This value is explicitly defined
* to be the same as {@link TextUtils#CAP_MODE_CHARACTERS}. Of course,
* this only affects languages where there are upper-case and lower-case letters.
*/
public static final int TYPE_TEXT_FLAG_CAP_CHARACTERS = 0x00001000;
/**
* Flag for {@link #TYPE_CLASS_TEXT}: capitalize the first character of
* every word. Overrides {@link #TYPE_TEXT_FLAG_CAP_SENTENCES}. This
* value is explicitly defined
* to be the same as {@link TextUtils#CAP_MODE_WORDS}. Of course,
* this only affects languages where there are upper-case and lower-case letters.
*/
public static final int TYPE_TEXT_FLAG_CAP_WORDS = 0x00002000;
/**
* Flag for {@link #TYPE_CLASS_TEXT}: capitalize the first character of
* each sentence. This value is explicitly defined
* to be the same as {@link TextUtils#CAP_MODE_SENTENCES}. For example
* in English it means to capitalize after a period and a space (note that other
* languages may have different characters for period, or not use spaces,
* or use different grammatical rules). Of course,
* this only affects languages where there are upper-case and lower-case letters.
*/
public static final int TYPE_TEXT_FLAG_CAP_SENTENCES = 0x00004000;
/**
* Flag for {@link #TYPE_CLASS_TEXT}: the user is entering free-form
* text that should have auto-correction applied to it. Without this flag,
* the IME will not try to correct typos. You should always set this flag
* unless you really expect users to type non-words in this field, for
* example to choose a name for a character in a game.
* Contrast this with {@link #TYPE_TEXT_FLAG_AUTO_COMPLETE} and
* {@link #TYPE_TEXT_FLAG_NO_SUGGESTIONS}:
* {@code TYPE_TEXT_FLAG_AUTO_CORRECT} means that the IME will try to
* auto-correct typos as the user is typing, but does not define whether
* the IME offers an interface to show suggestions.
*/
public static final int TYPE_TEXT_FLAG_AUTO_CORRECT = 0x00008000;
/**
* Flag for {@link #TYPE_CLASS_TEXT}: the text editor (which means
* the application) is performing auto-completion of the text being entered
* based on its own semantics, which it will present to the user as they type.
* This generally means that the input method should not be showing
* candidates itself, but can expect the editor to supply its own
* completions/candidates from
* {@link android.view.inputmethod.InputMethodSession#displayCompletions
* InputMethodSession.displayCompletions()} as a result of the editor calling
* {@link android.view.inputmethod.InputMethodManager#displayCompletions
* InputMethodManager.displayCompletions()}.
* Note the contrast with {@link #TYPE_TEXT_FLAG_AUTO_CORRECT} and
* {@link #TYPE_TEXT_FLAG_NO_SUGGESTIONS}:
* {@code TYPE_TEXT_FLAG_AUTO_COMPLETE} means the editor should show an
* interface for displaying suggestions, but instead of supplying its own
* it will rely on the Editor to pass completions/corrections.
*/
public static final int TYPE_TEXT_FLAG_AUTO_COMPLETE = 0x00010000;
/**
* Flag for {@link #TYPE_CLASS_TEXT}: multiple lines of text can be
* entered into the field. If this flag is not set, the text field
* will be constrained to a single line. The IME may also choose not to
* display an enter key when this flag is not set, as there should be no
* need to create new lines.
*/
public static final int TYPE_TEXT_FLAG_MULTI_LINE = 0x00020000;
/**
* Flag for {@link #TYPE_CLASS_TEXT}: the regular text view associated
* with this should not be multi-line, but when a fullscreen input method
* is providing text it should use multiple lines if it can.
*/
public static final int TYPE_TEXT_FLAG_IME_MULTI_LINE = 0x00040000;
/**
* Flag for {@link #TYPE_CLASS_TEXT}: the input method does not need to
* display any dictionary-based candidates. This is useful for text views that
* do not contain words from the language and do not benefit from any
* dictionary-based completions or corrections. It overrides the
* {@link #TYPE_TEXT_FLAG_AUTO_CORRECT} value when set.
* Please avoid using this unless you are certain this is what you want.
* Many input methods need suggestions to work well, for example the ones
* based on gesture typing. Consider clearing
* {@link #TYPE_TEXT_FLAG_AUTO_CORRECT} instead if you just do not
* want the IME to correct typos.
* Note the contrast with {@link #TYPE_TEXT_FLAG_AUTO_CORRECT} and
* {@link #TYPE_TEXT_FLAG_AUTO_COMPLETE}:
* {@code TYPE_TEXT_FLAG_NO_SUGGESTIONS} means the IME should never
* show an interface to display suggestions. Most IMEs will also take this to
* mean they should not try to auto-correct what the user is typing.
*/
public static final int TYPE_TEXT_FLAG_NO_SUGGESTIONS = 0x00080000;
// ----------------------------------------------------------------------
/**
* Default variation of {@link #TYPE_CLASS_TEXT}: plain old normal text.
*/
public static final int TYPE_TEXT_VARIATION_NORMAL = 0x00000000;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering a URI.
*/
public static final int TYPE_TEXT_VARIATION_URI = 0x00000010;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering an e-mail address.
*/
public static final int TYPE_TEXT_VARIATION_EMAIL_ADDRESS = 0x00000020;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering the subject line of
* an e-mail.
*/
public static final int TYPE_TEXT_VARIATION_EMAIL_SUBJECT = 0x00000030;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering a short, possibly informal
* message such as an instant message or a text message.
*/
public static final int TYPE_TEXT_VARIATION_SHORT_MESSAGE = 0x00000040;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering the content of a long, possibly
* formal message such as the body of an e-mail.
*/
public static final int TYPE_TEXT_VARIATION_LONG_MESSAGE = 0x00000050;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering the name of a person.
*/
public static final int TYPE_TEXT_VARIATION_PERSON_NAME = 0x00000060;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering a postal mailing address.
*/
public static final int TYPE_TEXT_VARIATION_POSTAL_ADDRESS = 0x00000070;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering a password.
*/
public static final int TYPE_TEXT_VARIATION_PASSWORD = 0x00000080;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering a password, which should
* be visible to the user.
*/
public static final int TYPE_TEXT_VARIATION_VISIBLE_PASSWORD = 0x00000090;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering text inside of a web form.
*/
public static final int TYPE_TEXT_VARIATION_WEB_EDIT_TEXT = 0x000000a0;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering text to filter contents
* of a list etc.
*/
public static final int TYPE_TEXT_VARIATION_FILTER = 0x000000b0;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering text for phonetic
* pronunciation, such as a phonetic name field in contacts. This is mostly
* useful for languages where one spelling may have several phonetic
* readings, like Japanese.
*/
public static final int TYPE_TEXT_VARIATION_PHONETIC = 0x000000c0;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering e-mail address inside
* of a web form. This was added in
* {@link android.os.Build.VERSION_CODES#HONEYCOMB}. An IME must target
* this API version or later to see this input type; if it doesn't, a request
* for this type will be seen as {@link #TYPE_TEXT_VARIATION_EMAIL_ADDRESS}
* when passed through {@link android.view.inputmethod.EditorInfo#makeCompatible(int)
* EditorInfo.makeCompatible(int)}.
*/
public static final int TYPE_TEXT_VARIATION_WEB_EMAIL_ADDRESS = 0x000000d0;
/**
* Variation of {@link #TYPE_CLASS_TEXT}: entering password inside
* of a web form. This was added in
* {@link android.os.Build.VERSION_CODES#HONEYCOMB}. An IME must target
* this API version or later to see this input type; if it doesn't, a request
* for this type will be seen as {@link #TYPE_TEXT_VARIATION_PASSWORD}
* when passed through {@link android.view.inputmethod.EditorInfo#makeCompatible(int)
* EditorInfo.makeCompatible(int)}.
*/
public static final int TYPE_TEXT_VARIATION_WEB_PASSWORD = 0x000000e0;
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
/**
* Class for numeric text. This class supports the following flags:
* {@link #TYPE_NUMBER_FLAG_SIGNED} and
* {@link #TYPE_NUMBER_FLAG_DECIMAL}. It also supports the following
* variations: {@link #TYPE_NUMBER_VARIATION_NORMAL} and
* {@link #TYPE_NUMBER_VARIATION_PASSWORD}.
*
IME authors: If you do not recognize
* the variation, normal should be assumed.
*/
public static final int TYPE_CLASS_NUMBER = 0x00000002;
/**
* Flag of {@link #TYPE_CLASS_NUMBER}: the number is signed, allowing
* a positive or negative sign at the start.
*/
public static final int TYPE_NUMBER_FLAG_SIGNED = 0x00001000;
/**
* Flag of {@link #TYPE_CLASS_NUMBER}: the number is decimal, allowing
* a decimal point to provide fractional values.
*/
public static final int TYPE_NUMBER_FLAG_DECIMAL = 0x00002000;
// ----------------------------------------------------------------------
/**
* Default variation of {@link #TYPE_CLASS_NUMBER}: plain normal
* numeric text. This was added in
* {@link android.os.Build.VERSION_CODES#HONEYCOMB}. An IME must target
* this API version or later to see this input type; if it doesn't, a request
* for this type will be dropped when passed through
* {@link android.view.inputmethod.EditorInfo#makeCompatible(int)
* EditorInfo.makeCompatible(int)}.
*/
public static final int TYPE_NUMBER_VARIATION_NORMAL = 0x00000000;
/**
* Variation of {@link #TYPE_CLASS_NUMBER}: entering a numeric password.
* This was added in {@link android.os.Build.VERSION_CODES#HONEYCOMB}. An
* IME must target this API version or later to see this input type; if it
* doesn't, a request for this type will be dropped when passed
* through {@link android.view.inputmethod.EditorInfo#makeCompatible(int)
* EditorInfo.makeCompatible(int)}.
*/
public static final int TYPE_NUMBER_VARIATION_PASSWORD = 0x00000010;
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
/**
* Class for a phone number. This class currently supports no variations
* or flags.
*/
public static final int TYPE_CLASS_PHONE = 0x00000003;
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
/**
* Class for dates and times. It supports the
* following variations:
* {@link #TYPE_DATETIME_VARIATION_NORMAL}
* {@link #TYPE_DATETIME_VARIATION_DATE}, and
* {@link #TYPE_DATETIME_VARIATION_TIME}.
*/
public static final int TYPE_CLASS_DATETIME = 0x00000004;
/**
* Default variation of {@link #TYPE_CLASS_DATETIME}: allows entering
* both a date and time.
*/
public static final int TYPE_DATETIME_VARIATION_NORMAL = 0x00000000;
/**
* Default variation of {@link #TYPE_CLASS_DATETIME}: allows entering
* only a date.
*/
public static final int TYPE_DATETIME_VARIATION_DATE = 0x00000010;
/**
* Default variation of {@link #TYPE_CLASS_DATETIME}: allows entering
* only a time.
*/
public static final int TYPE_DATETIME_VARIATION_TIME = 0x00000020;
}
由于位掩码方式又一个很大的问题，就是类型安全，如果不对类型安全控制后果会难以想象，因此枚举被用进去，以对参数类型进行控制，源码当中使用的是@IntDef，而EnumSet作为新的实现形式，在任何方面都比位掩码方式差不多或者更好，可读性，性能，以及类型安全等。权限逻辑如下：
public class NewPermission2 {
private EnumSet permissions = EnumSet.noneOf(Permission.class);
private enum Permission {
SELECT, INSERT, UPDATE, DELETE;
public static final EnumSet ALL_PERMISSIONS = EnumSet.allOf(Permission.class);
public static final EnumSet VIP_PERMISSIONS =
EnumSet.range(Permission.SELECT, Permission.UPDATE);
}
/**
* 重新设置权限
*/
public void setPermission(EnumSet s) {
this.permissions.clear();
this.permissions = s;
}
/**
* 删除一项或多项权限
*/
public void disable(Permission permission) {
permissions.remove(permission);
}
/**
* 是否拥某些权限
*/
public boolean isAllow(Permission s) {
return permissions.contains(s);
}
/**
* 是否是游客
*/
public boolean isVip(Permission s) {
return Permission.VIP_PERMISSIONS.contains(s);
}
} EnumSet具体实现可参看源码。个人觉得这种方式最大的好处，在于可控，无论是对业务逻辑很好理解，还是对代码实现的方便，各个方面来看，都是要比位掩码这种取巧方式的官方化。可是对于android开发的性能方面：
1 存在个别反射的身影
2 EnumSet是实现Set的集合类
基于以上两点，那么在设计用到Enumset的类的时候，还是需要谨慎一些，尽管官方给出了很可靠的保证。
另外一些讲得不错的博文：
http://eddmann.com/posts/using-bit-flags-and-enumsets-in-java/
http://dhruba.name/2008/12/31/effective-java-item-32-use-enumset-instead-of-bit-fields/