{"id":1228,"date":"2021-07-21T11:52:14","date_gmt":"2021-07-21T03:52:14","guid":{"rendered":"http:\/\/zerobox.org\/notes\/?p=1228"},"modified":"2021-07-21T11:53:50","modified_gmt":"2021-07-21T03:53:50","slug":"java-8-function-%e5%87%bd%e6%95%b0%e6%8e%a5%e5%8f%a3","status":"publish","type":"post","link":"http:\/\/zerobox.org\/notes\/1228.html","title":{"rendered":"Java 8 Function \u51fd\u6570\u63a5\u53e3"},"content":{"rendered":"\n

\u5728 Java 8 \u4e2d\uff0cFunction<\/strong> \u63a5\u53e3\u662f\u4e00\u4e2a\u51fd\u6570\u63a5\u53e3\uff0c\u5b83\u4f4d\u4e8e\u5305 java.util.function<\/code> \u4e0b\u3002 Function<\/code> \u63a5\u53e3\u4e2d\u5b9a\u4e49\u4e86\u4e00\u4e2a R apply(T t)<\/code> \u65b9\u6cd5\uff0c\u5b83\u53ef\u4ee5\u63a5\u53d7\u4e00\u4e2a\u6cdb\u578b T \u5bf9\u8c61\uff0c\u8fd4\u56de\u4e00\u4e2a\u6cdb\u578b R \u5bf9\u8c61\uff0c\u5373\u53c2\u6570\u7c7b\u578b\u548c\u8fd4\u56de\u7c7b\u578b\u53ef\u4ee5\u4e0d\u540c\u3002<\/p>\n\n\n\n

Function \u63a5\u53e3\u6e90\u7801\uff1a<\/p>\n\n\n\n

@FunctionalInterface\npublic interface Function<T, R> {\n\n    R apply(T t);\n\n    default <V> Function<V, R> compose(Function<? super V, ? extends T> before) {\n        Objects.requireNonNull(before);\n        return (V v) -> apply(before.apply(v));\n    }\n\n    default <V> Function<T, V> andThen(Function<? super R, ? extends V> after) {\n        Objects.requireNonNull(after);\n        return (T t) -> after.apply(apply(t));\n    }\n\n    static <T> Function<T, T> identity() {\n        return t -> t;\n    }\n}\n<\/code><\/pre>\n\n\n\n
1. Function apply<\/h2>\n\n\n\n
\u793a\u4f8b 1<\/strong>\uff1a\u8f93\u5165\u4e00\u4e2a\u5b57\u7b26\u4e32 <T> String<\/code>\uff0c \u8fd4\u56de\u5b57\u7b26\u4e32\u7684\u5927\u5199\u5f62\u5f0f <R> String<\/code>\u3002<\/p>\n\n\n\n
package com.wdbyte;\n\nimport java.util.function.Function;\n\npublic class Java8Function {\n    public static void main(String[] args) {\n        Function<String, String> toUpperCase = str -> str.toUpperCase();\n        String result = toUpperCase.apply(\"www.wdbyte.com\");\n        System.out.println(result);\n    }\n}\n<\/code><\/pre>\n\n\n\n
\u8f93\u51fa\u7ed3\u679c\uff1a<\/p>\n\n\n\n
WWW.WDBYTE.COM\n<\/code><\/pre>\n\n\n\n
\u793a\u4f8b 2<\/strong>\uff1a\u8f93\u5165\u4e00\u4e2a\u5b57\u7b26\u4e32 <T> String<\/code>\uff0c\u8fd4\u56de\u5b57\u7b26\u4e32\u7684\u957f\u5ea6 <R> Integer<\/code>\u3002<\/p>\n\n\n\n
package com.wdbyte;\n\nimport java.util.function.Function;\n\npublic class Java8FunctionLength {\n    public static void main(String[] args) {\n        Function<String, Integer> lengthFunction = str -> str.length();\n        Integer length = lengthFunction.apply(\"www.wdbyte.com\");\n        System.out.println(length);\n    }\n}\n<\/code><\/pre>\n\n\n\n
\u8f93\u51fa\u7ed3\u679c\uff1a<\/p>\n\n\n\n
14\n<\/code><\/pre>\n\n\n\n
2. Function andThen<\/h2>\n\n\n\n
Function \u51fd\u6570\u63a5\u53e3\u7684 andThen()<\/code> \u65b9\u6cd5\u53ef\u4ee5\u8ba9\u591a\u4e2a Function \u51fd\u6570\u8fde\u63a5\u4f7f\u7528\u3002<\/p>\n\n\n\n
\u793a\u4f8b<\/strong>\uff1a\u8f93\u5165\u4e00\u4e2a\u5b57\u7b26\u4e32\uff0c\u83b7\u53d6\u5b57\u7b26\u4e32\u7684\u957f\u5ea6\uff0c\u7136\u540e\u4e58\u4e0a 2\u3002<\/p>\n\n\n\n
package com.wdbyte;\n\nimport java.util.function.Function;\n\npublic class Java8FunctionAndThen {\n    public static void main(String[] args) {\n        Function<String, Integer> lengthFunction = str -> str.length();\n        Function<Integer, Integer> doubleFunction = length -> length * 2;\n        Integer doubleLength = lengthFunction.andThen(doubleFunction).apply(\"www.wdbyte.com\");\n        System.out.println(doubleLength);\n    }\n}\n<\/code><\/pre>\n\n\n\n
\u7ed3\u679c\uff1a<\/p>\n\n\n\n
28\n<\/code><\/pre>\n\n\n\n
3. List -> Map<\/h2>\n\n\n\n
\u793a\u4f8b<\/strong>\uff1a\u8f93\u5165\u4e00\u4e2a\u5b57\u7b26\u4e32 List \u96c6\u5408<T> List<String><\/code> \uff0c \u8fd4\u56de\u4e00\u4e2a key \u4e3a\u5b57\u7b26\u4e32\u672c\u8eab\uff0cValue \u4e3a\u5b57\u7b26\u4e32\u957f\u5ea6\u7684 Map<\/code>\u3002<\/p>\n\n\n\n
package com.wdbyte;\n\nimport java.util.Arrays;\nimport java.util.HashMap;\nimport java.util.List;\nimport java.util.Map;\nimport java.util.function.Function;\n\npublic class Java8FunctionListToMap {\n\n    public static void main(String[] args) {\n        List<String> list = Arrays.asList(\"java\", \"nodejs\", \"wdbyte.com\");\n        \/\/ lambda \u65b9\u5f0f\n        Function<String, Integer> lengthFunction = str -> str.length();\n        Map<String, Integer> listToMap = listToMap(list, lengthFunction);\n        System.out.println(listToMap);\n\n        \/\/ \u65b9\u6cd5\u5f15\u7528\u65b9\u5f0f\n        Map<String, Integer> listToMap2 = listToMap(list, String::length);\n        System.out.println(listToMap2);\n    }\n\n    public static <T, R> Map<T, R> listToMap(List<T> list, Function<T, R> function) {\n        HashMap<T, R> hashMap = new HashMap<>();\n        for (T t : list) {\n            hashMap.put(t, function.apply(t));\n        }\n        return hashMap;\n    }\n}\n<\/code><\/pre>\n\n\n\n
\u8f93\u51fa\u7ed3\u679c\uff1a<\/p>\n\n\n\n
{java=4, wdbyte.com=10, nodejs=6}\n{java=4, wdbyte.com=10, nodejs=6}\n<\/code><\/pre>\n\n\n\n
4. List -> List<Other><\/h2>\n\n\n\n
\u793a\u4f8b<\/strong> \uff1a\u8f93\u5165\u4e00\u4e2a\u5b57\u7b26\u4e32 List<\/code> \u96c6\u5408 <T> List<String><\/code> \uff0c\u8fd4\u56de\u5927\u5199<\/strong>\u5f62\u5f0f\u7684\u5b57\u7b26\u4e32 List<\/code> \u96c6\u5408\uff0c\u8fd4\u56de\u5c0f\u5199<\/strong>\u5f62\u5f0f\u7684\u5b57\u7b26\u4e32 List<\/code> \u96c6\u5408\u3002<\/p>\n\n\n\n
package com.wdbyte;\n\nimport java.util.ArrayList;\nimport java.util.Arrays;\nimport java.util.List;\nimport java.util.function.Function;\n\npublic class Java8FunctionString {\n\n    public static void main(String[] args) {\n        List<String> list = Arrays.asList(\"Java\", \"Nodejs\", \"Wdbyte.com\");\n        \/\/ \u65b9\u6cd5\u5f15\u7528\u65b9\u5f0f\n        List<String> upperList = map(list, String::toUpperCase);\n        List<String> lowerList = map(list, String::toLowerCase);\n        System.out.println(upperList);\n        System.out.println(lowerList);\n\n        \/\/ Lambda \u65b9\u5f0f\n        List<String> upperList2 = map(list, x -> x.toUpperCase());\n        List<String> lowerList2 = map(list, x -> x.toLowerCase());\n        System.out.println(upperList2);\n        System.out.println(lowerList2);\n\n    }\n\n    public static <T, R> List<R> map(List<T> list, Function<T, R> function) {\n        List<R> resultList = new ArrayList<>(list.size());\n        for (T t : list) {\n            resultList.add(function.apply(t));\n        }\n        return resultList;\n    }\n}\n<\/code><\/pre>\n\n\n\n
\u8f93\u51fa\u7ed3\u679c\uff1a<\/p>\n\n\n\n
[JAVA, NODEJS, WDBYTE.COM]\n[java, nodejs, wdbyte.com]\n[JAVA, NODEJS, WDBYTE.COM]\n[java, nodejs, wdbyte.com]\n\n\n<\/code><\/pre>\n\n\n\n
<\/p>\n\n\n\n
\u6587\u7ae0\u6765\u6e90\uff1ahttps:\/\/www.cnblogs.com\/niumoo\/p\/15034420.html<\/strong><\/h2>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
https:\/\/www.cnblogs.com\/niumoo\/p\/15034420.html<\/p>\n
\u7ee7\u7eed\u9605\u8bfb »<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[],"tags":[265,266],"class_list":["post-1228","post","type-post","status-publish","format-standard","hentry","tag-java-8","tag-266"],"views":251,"_links":{"self":[{"href":"http:\/\/zerobox.org\/notes\/wp-json\/wp\/v2\/posts\/1228","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/zerobox.org\/notes\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/zerobox.org\/notes\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/zerobox.org\/notes\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/zerobox.org\/notes\/wp-json\/wp\/v2\/comments?post=1228"}],"version-history":[{"count":0,"href":"http:\/\/zerobox.org\/notes\/wp-json\/wp\/v2\/posts\/1228\/revisions"}],"wp:attachment":[{"href":"http:\/\/zerobox.org\/notes\/wp-json\/wp\/v2\/media?parent=1228"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/zerobox.org\/notes\/wp-json\/wp\/v2\/categories?post=1228"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/zerobox.org\/notes\/wp-json\/wp\/v2\/tags?post=1228"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}