“`” \u8003\u5bdf\u70b9\uff1aJAVA\u6cdb\u578b<\/p>\n
\uff081\uff09\u6cdb\u578b\u4e2d\u4e0a\u754c\u548c\u4e0b\u754c\u7684\u5b9a\u4e49<\/p>\n
\u4e0a\u754c<? extend Fruit><\/p>\n
\u4e0b\u754c<? super Apple><\/p>\n
\uff082\uff09\u4e0a\u754c\u548c\u4e0b\u754c\u7684\u7279\u70b9<\/p>\n
\u4e0a\u754c\u7684list\u53ea\u80fdget\uff0c\u4e0d\u80fdadd\uff08\u786e\u5207\u5730\u8bf4\u4e0d\u80fdadd\u51fa\u9664null\u4e4b\u5916\u7684\u5bf9\u8c61\uff0c\u5305\u62ecObject\uff09<\/p>\n
\u4e0b\u754c\u7684list\u53ea\u80fdadd\uff0c\u4e0d\u80fdget<\/p>\n
\uff083\uff09\u793a\u4f8b\u4ee3\u7801<\/p>\n
<pre><code class=""language-java"" lang=""java"">import java.util.ArrayList;
\nimport java.util.List;<\/p>\n
class Fruit {}
\nclass Apple extends Fruit {}
\nclass Jonathan extends Apple {}
\nclass Orange extends Fruit {}<\/p>\n
public class CovariantArrays {
\n public static void main(String[] args) {
\n \/\/\u4e0a\u754c
\n List<? extends Fruit> flistTop = new ArrayList<Apple>();
\n flistTop.add(null);
\n \/\/add Fruit\u5bf9\u8c61\u4f1a\u62a5\u9519
\n \/\/flist.add(new Fruit());
\n Fruit fruit1 = flistTop.get(0);<\/p>\n
\/\/\u4e0b\u754c
\n List<? super Apple> flistBottem = new ArrayList<Apple>();
\n flistBottem.add(new Apple());
\n flistBottem.add(new Jonathan());
\n \/\/get Apple\u5bf9\u8c61\u4f1a\u62a5\u9519
\n \/\/Apple apple = flistBottem.get(0);
\n }
\n}
\n<\/code><\/pre><\/p>\n
\uff084\uff09\u4e0a\u754c<? extend Fruit> \uff0c\u8868\u793a\u6240\u6709\u7ee7\u627fFruit\u7684\u5b50\u7c7b\uff0c\u4f46\u662f\u5177\u4f53\u662f\u54ea\u4e2a\u5b50\u7c7b\uff0c\u65e0\u6cd5\u786e\u5b9a\uff0c\u6240\u4ee5\u8c03\u7528add\u7684\u65f6\u5019\uff0c\u8981add\u4ec0\u4e48\u7c7b\u578b\uff0c\u8c01\u4e5f\u4e0d\u77e5\u9053\u3002\u4f46\u662fget\u7684\u65f6\u5019\uff0c\u4e0d\u7ba1\u662f\u4ec0\u4e48\u5b50\u7c7b\uff0c\u4e0d\u7ba1\u8ffd\u6eaf\u591a\u5c11\u8f88\uff0c\u80af\u5b9a\u6709\u4e2a\u7236\u7c7b\u662fFruit\uff0c\u6240\u4ee5\uff0c\u6211\u90fd\u53ef\u4ee5\u7528\u6700\u5927\u7684\u7236\u7c7bFruit\u63a5\u7740\uff0c\u4e5f\u5c31\u662f\u628a\u6240\u6709\u7684\u5b50\u7c7b\u5411\u4e0a\u8f6c\u578b\u4e3aFruit\u3002<\/p>\n
\u4e0b\u754c<? super Apple>\uff0c\u8868\u793aApple\u7684\u6240\u6709\u7236\u7c7b\uff0c\u5305\u62ecFruit\uff0c\u4e00\u76f4\u53ef\u4ee5\u8ffd\u6eaf\u5230\u8001\u7956\u5b97Object \u3002\u90a3\u4e48\u5f53\u6211add\u7684\u65f6\u5019\uff0c\u6211\u4e0d\u80fdadd Apple\u7684\u7236\u7c7b\uff0c\u56e0\u4e3a\u4e0d\u80fd\u786e\u5b9aList\u91cc\u9762\u5b58\u653e\u7684\u5230\u5e95\u662f\u54ea\u4e2a\u7236\u7c7b\u3002\u4f46\u662f\u6211\u53ef\u4ee5add Apple\u53ca\u5176\u5b50\u7c7b\u3002\u56e0\u4e3a\u4e0d\u7ba1\u6211\u7684\u5b50\u7c7b\u662f\u4ec0\u4e48\u7c7b\u578b\uff0c\u5b83\u90fd\u53ef\u4ee5\u5411\u4e0a\u8f6c\u578b\u4e3aApple\u53ca\u5176\u6240\u6709\u7684\u7236\u7c7b\u751a\u81f3\u8f6c\u578b\u4e3aObject \u3002\u4f46\u662f\u5f53\u6211get\u7684\u65f6\u5019\uff0cApple\u7684\u7236\u7c7b\u8fd9\u4e48\u591a\uff0c\u6211\u7528\u4ec0\u4e48\u63a5\u7740\u5462\uff0c\u9664\u4e86Object\uff0c\u5176\u4ed6\u7684\u90fd\u63a5\u4e0d\u4f4f\u3002<\/p>\n
\u6240\u4ee5\uff0c\u5f52\u6839\u7ed3\u5e95\u53ef\u4ee5\u7528\u4e00\u53e5\u8bdd\u8868\u793a\uff0c\u90a3\u5c31\u662f\u7f16\u8bd1\u5668\u53ef\u4ee5\u652f\u6301\u5411\u4e0a\u8f6c\u578b\uff0c\u4f46\u4e0d\u652f\u6301\u5411\u4e0b\u8f6c\u578b\u3002\u5177\u4f53\u6765\u8bb2\uff0c\u6211\u53ef\u4ee5\u628aApple\u5bf9\u8c61\u8d4b\u503c\u7ed9Fruit\u7684\u5f15\u7528\uff0c\u4f46\u662f\u5982\u679c\u628aFruit\u5bf9\u8c61\u8d4b\u503c\u7ed9Apple\u7684\u5f15\u7528\u5c31\u5fc5\u987b\u5f97\u7528cast\u3002<\/p>\n
<pre><code> "“`
\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
“`” \u8003\u5bdf\u70b9\uff1aJAVA\u6cdb\u578b \uff081\uff09\u6cdb\u578b\u4e2d\u4e0a\u754c\u548c\u4e0b\u754c\u7684\u5b9a\u4e49 \u4e0a\u754c<? exten […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-38974","post","type-post","status-publish","format-standard","hentry","category-c"],"_links":{"self":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/38974","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/comments?post=38974"}],"version-history":[{"count":1,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/38974\/revisions"}],"predecessor-version":[{"id":38975,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/38974\/revisions\/38975"}],"wp:attachment":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/media?parent=38974"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/categories?post=38974"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/tags?post=38974"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}