{"id":2225,"date":"2018-02-08T16:14:22","date_gmt":"2018-02-08T08:14:22","guid":{"rendered":"https:\/\/ai.zhousir.top\/?p=2225"},"modified":"2018-02-10T10:51:07","modified_gmt":"2018-02-10T02:51:07","slug":"java-8-optional%e7%b1%bb%e6%b7%b1%e5%ba%a6%e8%a7%a3%e6%9e%90","status":"publish","type":"post","link":"https:\/\/ai.zhousir.top\/?p=2225","title":{"rendered":"Java 8 Optional\u7c7b\u6df1\u5ea6\u89e3\u6790"},"content":{"rendered":"

\u8eab\u4e3a\u4e00\u540dJava\u7a0b\u5e8f\u5458\uff0c\u5927\u5bb6\u53ef\u80fd\u90fd\u6709\u8fd9\u6837\u7684\u7ecf\u5386\uff1a\u8c03\u7528\u4e00\u4e2a\u65b9\u6cd5\u5f97\u5230\u4e86\u8fd4\u56de\u503c\u5374\u4e0d\u80fd\u76f4\u63a5\u5c06\u8fd4\u56de\u503c\u4f5c\u4e3a\u53c2\u6570\u53bb\u8c03\u7528\u522b\u7684\u65b9\u6cd5\u3002\u6211\u4eec\u9996\u5148\u8981\u5224\u65ad\u8fd9\u4e2a\u8fd4\u56de\u503c\u662f\u5426\u4e3anull\uff0c\u53ea\u6709\u5728\u975e\u7a7a\u7684\u524d\u63d0\u4e0b\u624d\u80fd\u5c06\u5176\u4f5c\u4e3a\u5176\u4ed6\u65b9\u6cd5\u7684\u53c2\u6570\u3002\u8fd9\u6b63\u662f\u4e00\u4e9b\u7c7b\u4f3cGuava<\/a>\u7684\u5916\u90e8API\u8bd5\u56fe\u89e3\u51b3\u7684\u95ee\u9898\u3002\u4e00\u4e9bJVM\u7f16\u7a0b\u8bed\u8a00\u6bd4\u5982Scala\u3001Ceylon\u7b49\u5df2\u7ecf\u5c06\u5bf9\u5728\u6838\u5fc3API\u4e2d\u89e3\u51b3\u4e86\u8fd9\u4e2a\u95ee\u9898\u3002\u5728\u6211\u7684\u524d\u4e00\u7bc7\u6587\u7ae0<\/a>\u4e2d\uff0c\u4ecb\u7ecd\u4e86Scala<\/a>\u662f\u5982\u4f55\u89e3\u51b3\u4e86\u8fd9\u4e2a\u95ee\u9898\u3002<\/p>\n

\u65b0\u7248\u672c\u7684Java\uff0c\u6bd4\u5982Java 8<\/a>\u5f15\u5165\u4e86\u4e00\u4e2a\u65b0\u7684Optional<\/a>\u7c7b\u3002Optional\u7c7b\u7684Javadoc\u63cf\u8ff0\u5982\u4e0b\uff1a<\/p>\n

\u8fd9\u662f\u4e00\u4e2a\u53ef\u4ee5\u4e3anull\u7684\u5bb9\u5668\u5bf9\u8c61\u3002\u5982\u679c\u503c\u5b58\u5728\u5219isPresent()\u65b9\u6cd5\u4f1a\u8fd4\u56detrue\uff0c\u8c03\u7528get()\u65b9\u6cd5\u4f1a\u8fd4\u56de\u8be5\u5bf9\u8c61\u3002<\/p><\/blockquote>\n

\u672c\u6587\u4f1a\u9010\u4e2a\u63a2\u8ba8Optional\u7c7b\u5305\u542b\u7684\u65b9\u6cd5\uff0c\u5e76\u901a\u8fc7\u4e00\u4e24\u4e2a\u793a\u4f8b\u5c55\u793a\u5982\u4f55\u4f7f\u7528\u3002<\/p>\n

of<\/strong><\/p>\n

\u4e3a\u975enull\u7684\u503c\u521b\u5efa\u4e00\u4e2aOptional\u3002<\/p><\/blockquote>\n

of\u65b9\u6cd5\u901a\u8fc7\u5de5\u5382\u65b9\u6cd5\u521b\u5efaOptional\u7c7b\u3002\u9700\u8981\u6ce8\u610f\u7684\u662f\uff0c\u521b\u5efa\u5bf9\u8c61\u65f6\u4f20\u5165\u7684\u53c2\u6570\u4e0d\u80fd\u4e3anull\u3002\u5982\u679c\u4f20\u5165\u53c2\u6570\u4e3anull\uff0c\u5219\u629b\u51faNullPointerException \u3002<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n<\/td>\n
\n
\n
\/\/\u8c03\u7528\u5de5\u5382\u65b9\u6cd5\u521b\u5efaOptional\u5b9e\u4f8b<\/code><\/div>\n
Optional<String> name = Optional.of(<\/code>\"Sanaulla\"<\/code>);<\/code><\/div>\n
\/\/\u4f20\u5165\u53c2\u6570\u4e3anull\uff0c\u629b\u51faNullPointerException.<\/code><\/div>\n
Optional<String> someNull = Optional.of(<\/code>null<\/code>);<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

ofNullable<\/strong><\/p>\n

\u4e3a\u6307\u5b9a\u7684\u503c\u521b\u5efa\u4e00\u4e2aOptional\uff0c\u5982\u679c\u6307\u5b9a\u7684\u503c\u4e3anull\uff0c\u5219\u8fd4\u56de\u4e00\u4e2a\u7a7a\u7684Optional\u3002<\/p><\/blockquote>\n

ofNullable\u4e0eof\u65b9\u6cd5\u76f8\u4f3c\uff0c\u552f\u4e00\u7684\u533a\u522b\u662f\u53ef\u4ee5\u63a5\u53d7\u53c2\u6570\u4e3anull\u7684\u60c5\u51b5\u3002\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n<\/td>\n
\n
\n
\/\/\u4e0b\u9762\u521b\u5efa\u4e86\u4e00\u4e2a\u4e0d\u5305\u542b\u4efb\u4f55\u503c\u7684Optional\u5b9e\u4f8b<\/code><\/div>\n
\/\/\u4f8b\u5982\uff0c\u503c\u4e3a'null'<\/code><\/div>\n
Optional empty = Optional.ofNullable(<\/code>null<\/code>);<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

isPresent<\/strong><\/p>\n

\u975e\u5e38\u5bb9\u6613\u7406\u89e3<\/p>\n

\u5982\u679c\u503c\u5b58\u5728\u8fd4\u56detrue\uff0c\u5426\u5219\u8fd4\u56defalse\u3002<\/p><\/blockquote>\n

\u7c7b\u4f3c\u4e0b\u9762\u7684\u4ee3\u7801\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n<\/td>\n
\n
\n
\/\/isPresent\u65b9\u6cd5\u7528\u6765\u68c0\u67e5Optional\u5b9e\u4f8b\u4e2d\u662f\u5426\u5305\u542b\u503c<\/code><\/div>\n
if<\/code> (name.isPresent()) {<\/code><\/div>\n
\u00a0\u00a0<\/code>\/\/\u5728Optional\u5b9e\u4f8b\u5185\u8c03\u7528get()\u8fd4\u56de\u5df2\u5b58\u5728\u7684\u503c<\/code><\/div>\n
\u00a0\u00a0<\/code>System.out.println(name.get());<\/code>\/\/\u8f93\u51faSanaulla<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

get<\/strong><\/p>\n

\u5982\u679cOptional\u6709\u503c\u5219\u5c06\u5176\u8fd4\u56de\uff0c\u5426\u5219\u629b\u51faNoSuchElementException\u3002<\/p><\/blockquote>\n

\u4e0a\u9762\u7684\u793a\u4f8b\u4e2d\uff0cget\u65b9\u6cd5\u7528\u6765\u5f97\u5230Optional\u5b9e\u4f8b\u4e2d\u7684\u503c\u3002\u4e0b\u9762\u6211\u4eec\u770b\u4e00\u4e2a\u629b\u51faNoSuchElementException\u7684\u4f8b\u5b50\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n
6<\/div>\n
7<\/div>\n<\/td>\n
\n
\n
\/\/\u6267\u884c\u4e0b\u9762\u7684\u4ee3\u7801\u4f1a\u8f93\u51fa\uff1aNo value present <\/code><\/div>\n
try<\/code> {<\/code><\/div>\n
\u00a0\u00a0<\/code>\/\/\u5728\u7a7a\u7684Optional\u5b9e\u4f8b\u4e0a\u8c03\u7528get()\uff0c\u629b\u51faNoSuchElementException<\/code><\/div>\n
\u00a0\u00a0<\/code>System.out.println(empty.get());<\/code><\/div>\n
} <\/code>catch<\/code> (NoSuchElementException ex) {<\/code><\/div>\n
\u00a0\u00a0<\/code>System.out.println(ex.getMessage());<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

ifPresent<\/strong><\/p>\n

\u5982\u679cOptional\u5b9e\u4f8b\u6709\u503c\u5219\u4e3a\u5176\u8c03\u7528consumer\uff0c\u5426\u5219\u4e0d\u505a\u5904\u7406<\/p><\/blockquote>\n

\u8981\u7406\u89e3ifPresent\u65b9\u6cd5\uff0c\u9996\u5148\u9700\u8981\u4e86\u89e3Consumer\u7c7b<\/a>\u3002\u7b80\u7b54\u5730\u8bf4\uff0cConsumer\u7c7b\u5305\u542b\u4e00\u4e2a\u62bd\u8c61\u65b9\u6cd5\u3002\u8be5\u62bd\u8c61\u65b9\u6cd5\u5bf9\u4f20\u5165\u7684\u503c\u8fdb\u884c\u5904\u7406\uff0c\u4f46\u6ca1\u6709\u8fd4\u56de\u503c\u3002Java8<\/a>\u652f\u6301\u4e0d\u7528\u63a5\u53e3\u76f4\u63a5\u901a\u8fc7lambda\u8868\u8fbe\u5f0f<\/a>\u4f20\u5165\u53c2\u6570\u3002<\/p>\n

\u5982\u679cOptional\u5b9e\u4f8b\u6709\u503c\uff0c\u8c03\u7528ifPresent()\u53ef\u4ee5\u63a5\u53d7\u63a5\u53e3\u6bb5\u6216lambda\u8868\u8fbe\u5f0f\u3002\u7c7b\u4f3c\u4e0b\u9762\u7684\u4ee3\u7801\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n<\/td>\n
\n
\n
\/\/ifPresent\u65b9\u6cd5\u63a5\u53d7lambda\u8868\u8fbe\u5f0f\u4f5c\u4e3a\u53c2\u6570\u3002<\/code><\/div>\n
\/\/lambda\u8868\u8fbe\u5f0f\u5bf9Optional\u7684\u503c\u8c03\u7528consumer\u8fdb\u884c\u5904\u7406\u3002<\/code><\/div>\n
name.ifPresent((value) -> {<\/code><\/div>\n
\u00a0\u00a0<\/code>System.out.println(<\/code>\"The length of the value is: \"<\/code> + value.length());<\/code><\/div>\n
});<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

orElse<\/strong><\/p>\n

\u5982\u679c\u6709\u503c\u5219\u5c06\u5176\u8fd4\u56de\uff0c\u5426\u5219\u8fd4\u56de\u6307\u5b9a\u7684\u5176\u5b83\u503c\u3002<\/p><\/blockquote>\n

\u5982\u679cOptional\u5b9e\u4f8b\u6709\u503c\u5219\u5c06\u5176\u8fd4\u56de\uff0c\u5426\u5219\u8fd4\u56deorElse\u65b9\u6cd5\u4f20\u5165\u7684\u53c2\u6570\u3002\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n
6<\/div>\n<\/td>\n
\n
\n
\/\/\u5982\u679c\u503c\u4e0d\u4e3anull\uff0corElse\u65b9\u6cd5\u8fd4\u56deOptional\u5b9e\u4f8b\u7684\u503c\u3002<\/code><\/div>\n
\/\/\u5982\u679c\u4e3anull\uff0c\u8fd4\u56de\u4f20\u5165\u7684\u6d88\u606f\u3002<\/code><\/div>\n
\/\/\u8f93\u51fa\uff1aThere is no value present!<\/code><\/div>\n
System.out.println(empty.orElse(<\/code>\"There is no value present!\"<\/code>));<\/code><\/div>\n
\/\/\u8f93\u51fa\uff1aSanaulla<\/code><\/div>\n
System.out.println(name.orElse(<\/code>\"There is some value!\"<\/code>));<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

orElseGet<\/strong><\/p>\n

orElseGet\u4e0eorElse\u65b9\u6cd5\u7c7b\u4f3c\uff0c\u533a\u522b\u5728\u4e8e\u5f97\u5230\u7684\u9ed8\u8ba4\u503c\u3002orElse\u65b9\u6cd5\u5c06\u4f20\u5165\u7684\u5b57\u7b26\u4e32\u4f5c\u4e3a\u9ed8\u8ba4\u503c\uff0corElseGet\u65b9\u6cd5\u53ef\u4ee5\u63a5\u53d7Supplier\u63a5\u53e3<\/a>\u7684\u5b9e\u73b0\u7528\u6765\u751f\u6210\u9ed8\u8ba4\u503c\u3002\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n
6<\/div>\n<\/td>\n
\n
\n
\/\/orElseGet\u4e0eorElse\u65b9\u6cd5\u7c7b\u4f3c\uff0c\u533a\u522b\u5728\u4e8eorElse\u4f20\u5165\u7684\u662f\u9ed8\u8ba4\u503c\uff0c<\/code><\/div>\n
\/\/orElseGet\u53ef\u4ee5\u63a5\u53d7\u4e00\u4e2alambda\u8868\u8fbe\u5f0f\u751f\u6210\u9ed8\u8ba4\u503c\u3002<\/code><\/div>\n
\/\/\u8f93\u51fa\uff1aDefault Value<\/code><\/div>\n
System.out.println(empty.orElseGet(() -> <\/code>\"Default Value\"<\/code>));<\/code><\/div>\n
\/\/\u8f93\u51fa\uff1aSanaulla<\/code><\/div>\n
System.out.println(name.orElseGet(() -> <\/code>\"Default Value\"<\/code>));<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

orElseThrow<\/strong><\/p>\n

\u5982\u679c\u6709\u503c\u5219\u5c06\u5176\u8fd4\u56de\uff0c\u5426\u5219\u629b\u51fasupplier\u63a5\u53e3\u521b\u5efa\u7684\u5f02\u5e38\u3002<\/p><\/blockquote>\n

\u5728orElseGet\u65b9\u6cd5\u4e2d\uff0c\u6211\u4eec\u4f20\u5165\u4e00\u4e2aSupplier\u63a5\u53e3<\/a>\u3002\u7136\u800c\uff0c\u5728orElseThrow\u4e2d\u6211\u4eec\u53ef\u4ee5\u4f20\u5165\u4e00\u4e2alambda\u8868\u8fbe\u5f0f\u6216\u65b9\u6cd5\uff0c\u5982\u679c\u503c\u4e0d\u5b58\u5728\u6765\u629b\u51fa\u5f02\u5e38\u3002\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n
6<\/div>\n
7<\/div>\n
8<\/div>\n
9<\/div>\n<\/td>\n
\n
\n
try<\/code> {<\/code><\/div>\n
\u00a0\u00a0<\/code>\/\/orElseThrow\u4e0eorElse\u65b9\u6cd5\u7c7b\u4f3c\u3002\u4e0e\u8fd4\u56de\u9ed8\u8ba4\u503c\u4e0d\u540c\uff0c<\/code><\/div>\n
\u00a0\u00a0<\/code>\/\/orElseThrow\u4f1a\u629b\u51falambda\u8868\u8fbe\u5f0f\u6216\u65b9\u6cd5\u751f\u6210\u7684\u5f02\u5e38 <\/code><\/div>\n
<\/div>\n
\u00a0\u00a0<\/code>empty.orElseThrow(ValueAbsentException::<\/code>new<\/code>);<\/code><\/div>\n
} <\/code>catch<\/code> (Throwable ex) {<\/code><\/div>\n
\u00a0\u00a0<\/code>\/\/\u8f93\u51fa: No value present in the Optional instance<\/code><\/div>\n
\u00a0\u00a0<\/code>System.out.println(ex.getMessage());<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

ValueAbsentException\u5b9a\u4e49\u5982\u4e0b\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
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4<\/div>\n
5<\/div>\n
6<\/div>\n
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9<\/div>\n
10<\/div>\n
11<\/div>\n
12<\/div>\n
13<\/div>\n
14<\/div>\n
15<\/div>\n<\/td>\n
\n
\n
class<\/code> ValueAbsentException <\/code>extends<\/code> Throwable {<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0<\/code>public<\/code> ValueAbsentException() {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>super<\/code>();<\/code><\/div>\n
\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0<\/code>public<\/code> ValueAbsentException(String msg) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>super<\/code>(msg);<\/code><\/div>\n
\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0<\/code>@Override<\/code><\/div>\n
\u00a0\u00a0<\/code>public<\/code> String getMessage() {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code> \"No value present in the Optional instance\"<\/code>;<\/code><\/div>\n
\u00a0\u00a0<\/code>}<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

map<\/strong><\/p>\n

map\u65b9\u6cd5\u6587\u6863\u8bf4\u660e\u5982\u4e0b\uff1a<\/p>\n

\u5982\u679c\u6709\u503c\uff0c\u5219\u5bf9\u5176\u6267\u884c\u8c03\u7528mapping\u51fd\u6570\u5f97\u5230\u8fd4\u56de\u503c\u3002\u5982\u679c\u8fd4\u56de\u503c\u4e0d\u4e3anull\uff0c\u5219\u521b\u5efa\u5305\u542bmapping\u8fd4\u56de\u503c\u7684Optional\u4f5c\u4e3amap\u65b9\u6cd5\u8fd4\u56de\u503c\uff0c\u5426\u5219\u8fd4\u56de\u7a7aOptional\u3002<\/p><\/blockquote>\n

map\u65b9\u6cd5\u7528\u6765\u5bf9Optional\u5b9e\u4f8b\u7684\u503c\u6267\u884c\u4e00\u7cfb\u5217\u64cd\u4f5c\u3002\u901a\u8fc7\u4e00\u7ec4\u5b9e\u73b0\u4e86Function\u63a5\u53e3\u7684lambda\u8868\u8fbe\u5f0f\u4f20\u5165\u64cd\u4f5c\u3002\u5982\u679c\u4f60\u4e0d\u719f\u6089Function\u63a5\u53e3\uff0c\u53ef\u4ee5\u53c2\u8003\u6211\u7684\u8fd9\u7bc7\u535a\u5ba2<\/a>\u3002map\u65b9\u6cd5\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n

\n
\n\n\n\n
\n
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4<\/div>\n<\/td>\n
\n
\n
\/\/map\u65b9\u6cd5\u6267\u884c\u4f20\u5165\u7684lambda\u8868\u8fbe\u5f0f\u53c2\u6570\u5bf9Optional\u5b9e\u4f8b\u7684\u503c\u8fdb\u884c\u4fee\u6539\u3002<\/code><\/div>\n
\/\/\u4e3alambda\u8868\u8fbe\u5f0f\u7684\u8fd4\u56de\u503c\u521b\u5efa\u65b0\u7684Optional\u5b9e\u4f8b\u4f5c\u4e3amap\u65b9\u6cd5\u7684\u8fd4\u56de\u503c\u3002<\/code><\/div>\n
Optional<String> upperName = name.map((value) -> value.toUpperCase());<\/code><\/div>\n
System.out.println(upperName.orElse(<\/code>\"No value found\"<\/code>));<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

flatMap<\/strong><\/p>\n

\u5982\u679c\u6709\u503c\uff0c\u4e3a\u5176\u6267\u884cmapping\u51fd\u6570\u8fd4\u56deOptional\u7c7b\u578b\u8fd4\u56de\u503c\uff0c\u5426\u5219\u8fd4\u56de\u7a7aOptional\u3002flatMap\u4e0emap\uff08Funtion\uff09\u65b9\u6cd5\u7c7b\u4f3c\uff0c\u533a\u522b\u5728\u4e8eflatMap\u4e2d\u7684mapper\u8fd4\u56de\u503c\u5fc5\u987b\u662fOptional\u3002\u8c03\u7528\u7ed3\u675f\u65f6\uff0cflatMap\u4e0d\u4f1a\u5bf9\u7ed3\u679c\u7528Optional\u5c01\u88c5\u3002<\/p><\/blockquote>\n

flatMap\u65b9\u6cd5\u4e0emap\u65b9\u6cd5\u7c7b\u4f3c\uff0c\u533a\u522b\u5728\u4e8emapping\u51fd\u6570\u7684\u8fd4\u56de\u503c\u4e0d\u540c\u3002map\u65b9\u6cd5\u7684mapping\u51fd\u6570\u8fd4\u56de\u503c\u53ef\u4ee5\u662f\u4efb\u4f55\u7c7b\u578bT\uff0c\u800cflatMap\u65b9\u6cd5\u7684mapping\u51fd\u6570\u5fc5\u987b\u662fOptional\u3002<\/p>\n

\u53c2\u7167map\u51fd\u6570\uff0c\u4f7f\u7528flatMap\u91cd\u5199\u7684\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n<\/td>\n
\n
\n
\/\/flatMap\u4e0emap\uff08Function\uff09\u975e\u5e38\u7c7b\u4f3c\uff0c\u533a\u522b\u5728\u4e8e\u4f20\u5165\u65b9\u6cd5\u7684lambda\u8868\u8fbe\u5f0f\u7684\u8fd4\u56de\u7c7b\u578b\u3002<\/code><\/div>\n
\/\/map\u65b9\u6cd5\u4e2d\u7684lambda\u8868\u8fbe\u5f0f\u8fd4\u56de\u503c\u53ef\u4ee5\u662f\u4efb\u610f\u7c7b\u578b\uff0c\u5728map\u51fd\u6570\u8fd4\u56de\u4e4b\u524d\u4f1a\u5305\u88c5\u4e3aOptional\u3002 <\/code><\/div>\n
\/\/\u4f46flatMap\u65b9\u6cd5\u4e2d\u7684lambda\u8868\u8fbe\u5f0f\u8fd4\u56de\u503c\u5fc5\u987b\u662fOptionl\u5b9e\u4f8b\u3002 <\/code><\/div>\n
upperName = name.flatMap((value) -> Optional.of(value.toUpperCase()));<\/code><\/div>\n
System.out.println(upperName.orElse(<\/code>\"No value found\"<\/code>));<\/code>\/\/\u8f93\u51faSANAULLA<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

filter<\/strong><\/p>\n

filter\u4e2a\u65b9\u6cd5\u901a\u8fc7\u4f20\u5165\u9650\u5b9a\u6761\u4ef6\u5bf9Optional\u5b9e\u4f8b\u7684\u503c\u8fdb\u884c\u8fc7\u6ee4\u3002\u6587\u6863\u63cf\u8ff0\u5982\u4e0b\uff1a<\/p>\n

\u5982\u679c\u6709\u503c\u5e76\u4e14\u6ee1\u8db3\u65ad\u8a00\u6761\u4ef6\u8fd4\u56de\u5305\u542b\u8be5\u503c\u7684Optional\uff0c\u5426\u5219\u8fd4\u56de\u7a7aOptional\u3002<\/p><\/blockquote>\n

\u8bfb\u5230\u8fd9\u91cc\uff0c\u53ef\u80fd\u4f60\u5df2\u7ecf\u77e5\u9053\u5982\u4f55\u4e3afilter\u65b9\u6cd5\u4f20\u5165\u4e00\u6bb5\u4ee3\u7801\u3002\u662f\u7684\uff0c\u8fd9\u91cc\u53ef\u4ee5\u4f20\u5165\u4e00\u4e2alambda\u8868\u8fbe\u5f0f\u3002\u5bf9\u4e8efilter\u51fd\u6570\u6211\u4eec\u5e94\u8be5\u4f20\u5165\u5b9e\u73b0\u4e86Predicate\u63a5\u53e3\u7684lambda\u8868\u8fbe\u5f0f\u3002\u5982\u679c\u4f60\u4e0d\u719f\u6089Predicate\u63a5\u53e3\uff0c\u53ef\u4ee5\u53c2\u8003\u8fd9\u7bc7\u6587\u7ae0<\/a>\u3002<\/p>\n

\u73b0\u5728\u6211\u6765\u770b\u770bfilter\u7684\u5404\u79cd\u7528\u6cd5\uff0c\u4e0b\u9762\u7684\u793a\u4f8b\u4ecb\u7ecd\u4e86\u6ee1\u8db3\u9650\u5b9a\u6761\u4ef6\u548c\u4e0d\u6ee1\u8db3\u4e24\u79cd\u60c5\u51b5\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
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3<\/div>\n
4<\/div>\n
5<\/div>\n
6<\/div>\n
7<\/div>\n
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9<\/div>\n
10<\/div>\n<\/td>\n
\n
\n
\/\/filter\u65b9\u6cd5\u68c0\u67e5\u7ed9\u5b9a\u7684Option\u503c\u662f\u5426\u6ee1\u8db3\u67d0\u4e9b\u6761\u4ef6\u3002<\/code><\/div>\n
\/\/\u5982\u679c\u6ee1\u8db3\u5219\u8fd4\u56de\u540c\u4e00\u4e2aOption\u5b9e\u4f8b\uff0c\u5426\u5219\u8fd4\u56de\u7a7aOptional\u3002<\/code><\/div>\n
Optional<String> longName = name.filter((value) -> value.length() > <\/code>6<\/code>);<\/code><\/div>\n
System.out.println(longName.orElse(<\/code>\"The name is less than 6 characters\"<\/code>));<\/code>\/\/\u8f93\u51faSanaulla<\/code><\/div>\n
<\/div>\n
\/\/\u53e6\u4e00\u4e2a\u4f8b\u5b50\u662fOptional\u503c\u4e0d\u6ee1\u8db3filter\u6307\u5b9a\u7684\u6761\u4ef6\u3002<\/code><\/div>\n
Optional<String> anotherName = Optional.of(<\/code>\"Sana\"<\/code>);<\/code><\/div>\n
Optional<String> shortName = anotherName.filter((value) -> value.length() > <\/code>6<\/code>);<\/code><\/div>\n
\/\/\u8f93\u51fa\uff1aname\u957f\u5ea6\u4e0d\u8db36\u5b57\u7b26<\/code><\/div>\n
System.out.println(shortName.orElse(<\/code>\"The name is less than 6 characters\"<\/code>));<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

\u4ee5\u4e0a\uff0c\u6211\u4eec\u4ecb\u7ecd\u4e86Optional\u7c7b\u7684\u5404\u4e2a\u65b9\u6cd5\u3002\u4e0b\u9762\u901a\u8fc7\u4e00\u4e2a\u5b8c\u6574\u7684\u793a\u4f8b\u5bf9\u7528\u6cd5\u96c6\u4e2d\u5c55\u793a\uff1a<\/p>\n

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\n
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\n
\n
public<\/code> class<\/code> OptionalDemo {<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0<\/code>public<\/code> static<\/code> void<\/code> main(String[] args) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/\u521b\u5efaOptional\u5b9e\u4f8b\uff0c\u4e5f\u53ef\u4ee5\u901a\u8fc7\u65b9\u6cd5\u8fd4\u56de\u503c\u5f97\u5230\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>Optional<String> name = Optional.of(<\/code>\"Sanaulla\"<\/code>);<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/\u521b\u5efa\u6ca1\u6709\u503c\u7684Optional\u5b9e\u4f8b\uff0c\u4f8b\u5982\u503c\u4e3a'null'<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>Optional empty = Optional.ofNullable(<\/code>null<\/code>);<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/isPresent\u65b9\u6cd5\u7528\u6765\u68c0\u67e5Optional\u5b9e\u4f8b\u662f\u5426\u6709\u503c\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code> (name.isPresent()) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>\/\/\u8c03\u7528get()\u8fd4\u56deOptional\u503c\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(name.get());<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>try<\/code> {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>\/\/\u5728Optional\u5b9e\u4f8b\u4e0a\u8c03\u7528get()\u629b\u51faNoSuchElementException\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(empty.get());<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>} <\/code>catch<\/code> (NoSuchElementException ex) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(ex.getMessage());<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/ifPresent\u65b9\u6cd5\u63a5\u53d7lambda\u8868\u8fbe\u5f0f\u53c2\u6570\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/\u5982\u679cOptional\u503c\u4e0d\u4e3a\u7a7a\uff0clambda\u8868\u8fbe\u5f0f\u4f1a\u5904\u7406\u5e76\u5728\u5176\u4e0a\u6267\u884c\u64cd\u4f5c\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>name.ifPresent((value) -> {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(<\/code>\"The length of the value is: \"<\/code> + value.length());<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>});<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/\u5982\u679c\u6709\u503corElse\u65b9\u6cd5\u4f1a\u8fd4\u56deOptional\u5b9e\u4f8b\uff0c\u5426\u5219\u8fd4\u56de\u4f20\u5165\u7684\u9519\u8bef\u4fe1\u606f\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(empty.orElse(<\/code>\"There is no value present!\"<\/code>));<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(name.orElse(<\/code>\"There is some value!\"<\/code>));<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/orElseGet\u4e0eorElse\u7c7b\u4f3c\uff0c\u533a\u522b\u5728\u4e8e\u4f20\u5165\u7684\u9ed8\u8ba4\u503c\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/orElseGet\u63a5\u53d7lambda\u8868\u8fbe\u5f0f\u751f\u6210\u9ed8\u8ba4\u503c\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(empty.orElseGet(() -> <\/code>\"Default Value\"<\/code>));<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(name.orElseGet(() -> <\/code>\"Default Value\"<\/code>));<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>try<\/code> {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>\/\/orElseThrow\u4e0eorElse\u65b9\u6cd5\u7c7b\u4f3c\uff0c\u533a\u522b\u5728\u4e8e\u8fd4\u56de\u503c\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>\/\/orElseThrow\u629b\u51fa\u7531\u4f20\u5165\u7684lambda\u8868\u8fbe\u5f0f\/\u65b9\u6cd5\u751f\u6210\u5f02\u5e38\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>empty.orElseThrow(ValueAbsentException::<\/code>new<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>} <\/code>catch<\/code> (Throwable ex) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(ex.getMessage());<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/map\u65b9\u6cd5\u901a\u8fc7\u4f20\u5165\u7684lambda\u8868\u8fbe\u5f0f\u4fee\u6539Optonal\u5b9e\u4f8b\u9ed8\u8ba4\u503c\u3002 <\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/lambda\u8868\u8fbe\u5f0f\u8fd4\u56de\u503c\u4f1a\u5305\u88c5\u4e3aOptional\u5b9e\u4f8b\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>Optional<String> upperName = name.map((value) -> value.toUpperCase());<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(upperName.orElse(<\/code>\"No value found\"<\/code>));<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/flatMap\u4e0emap\uff08Funtion\uff09\u975e\u5e38\u76f8\u4f3c\uff0c\u533a\u522b\u5728\u4e8elambda\u8868\u8fbe\u5f0f\u7684\u8fd4\u56de\u503c\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/map\u65b9\u6cd5\u7684lambda\u8868\u8fbe\u5f0f\u8fd4\u56de\u503c\u53ef\u4ee5\u662f\u4efb\u4f55\u7c7b\u578b\uff0c\u4f46\u662f\u8fd4\u56de\u503c\u4f1a\u5305\u88c5\u6210Optional\u5b9e\u4f8b\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/\u4f46\u662fflatMap\u65b9\u6cd5\u7684lambda\u8fd4\u56de\u503c\u603b\u662fOptional\u7c7b\u578b\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>upperName = name.flatMap((value) -> Optional.of(value.toUpperCase()));<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(upperName.orElse(<\/code>\"No value found\"<\/code>));<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/filter\u65b9\u6cd5\u68c0\u67e5Optiona\u503c\u662f\u5426\u6ee1\u8db3\u7ed9\u5b9a\u6761\u4ef6\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/\u5982\u679c\u6ee1\u8db3\u8fd4\u56deOptional\u5b9e\u4f8b\u503c\uff0c\u5426\u5219\u8fd4\u56de\u7a7aOptional\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>Optional<String> longName = name.filter((value) -> value.length() > <\/code>6<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(longName.orElse(<\/code>\"The name is less than 6 characters\"<\/code>));<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/\u53e6\u4e00\u4e2a\u793a\u4f8b\uff0cOptional\u503c\u4e0d\u6ee1\u8db3\u7ed9\u5b9a\u6761\u4ef6\u3002<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>Optional<String> anotherName = Optional.of(<\/code>\"Sana\"<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>Optional<String> shortName = anotherName.filter((value) -> value.length() > <\/code>6<\/code>);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>System.out.println(shortName.orElse(<\/code>\"The name is less than 6 characters\"<\/code>));<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0<\/code>}<\/code><\/div>\n
<\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

\u4e0a\u8ff0\u4ee3\u7801\u8f93\u51fa\u5982\u4e0b\uff1a<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n
6<\/div>\n
7<\/div>\n
8<\/div>\n
9<\/div>\n
10<\/div>\n
11<\/div>\n
12<\/div>\n<\/td>\n
\n
\n
Sanaulla<\/code><\/div>\n
No value present<\/code><\/div>\n
The length of the value is: 8<\/code><\/div>\n
There is no value present!<\/code><\/div>\n
Sanaulla<\/code><\/div>\n
Default Value<\/code><\/div>\n
Sanaulla<\/code><\/div>\n
No value present <\/code>in<\/code> the Optional instance<\/code><\/div>\n
SANAULLA<\/code><\/div>\n
SANAULLA<\/code><\/div>\n
Sanaulla<\/code><\/div>\n
The name is <\/code>less<\/code> than 6 characters<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

\u539f\u6587\u94fe\u63a5\uff1a\u00a0javacodegeeks<\/a>\u00a0\u7ffb\u8bd1\uff1a\u00a0ImportNew.com\u00a0<\/a>–\u00a0\u9ad8\u4fca\u9633<\/a>
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