{"id":171279,"date":"2024-05-08T17:25:58","date_gmt":"2024-05-08T09:25:58","guid":{"rendered":"https:\/\/docs.pingcode.com\/ask\/ask-ask\/171279.html"},"modified":"2024-05-08T17:26:01","modified_gmt":"2024-05-08T09:26:01","slug":"java-10-var-%e5%85%b3%e9%94%ae%e5%ad%97%e5%9c%a8%e5%bc%80%e5%8f%91%e4%b8%ad%e6%9c%89%e5%93%aa%e4%ba%9b%e5%ba%94%e7%94%a8","status":"publish","type":"post","link":"https:\/\/docs.pingcode.com\/ask\/171279.html","title":{"rendered":"Java 10 var \u5173\u952e\u5b57\u5728\u5f00\u53d1\u4e2d\u6709\u54ea\u4e9b\u5e94\u7528"},"content":{"rendered":"

\"Java<\/p>\n

Java 10\u5f15\u5165\u7684var\u5173\u952e\u5b57<\/strong>\u4e3b\u8981\u7528\u4e8e\u5c40\u90e8\u53d8\u91cf\u7684\u7c7b\u578b\u63a8\u65ad\uff0c\u5373\u5728\u5c40\u90e8\u53d8\u7ea7\u522b\u53ef\u4ee5\u4e0d\u663e\u5f0f\u58f0\u660e\u53d8\u91cf\u7684\u7c7b\u578b\uff0c\u800c\u662f\u901a\u8fc7\u53d8\u91cf\u7684\u521d\u59cb\u503c\u8ba9\u7f16\u8bd1\u5668\u81ea\u52a8\u63a8\u65ad\u5176\u7c7b\u578b\u3002\u8fd9\u6837\u505a\u7684\u597d\u5904\u5305\u62ec\u4f7f\u4ee3\u7801\u66f4\u52a0\u7b80\u6d01\u3001\u63d0\u9ad8\u5f00\u53d1\u6548\u7387\u3001\u964d\u4f4e\u6a21\u677f\u4ee3\u7801\u7684\u5197\u4f59\u548c\u589e\u5f3a\u4ee3\u7801\u7684\u53ef\u8bfb\u6027\u3002\u7279\u522b\u662f\u5728\u5904\u7406\u8f83\u957f\u7684\u6cdb\u578b\u7c7b\u578b\u65f6\uff0cvar\u5173\u952e\u5b57\u7684\u4f7f\u7528\u53ef\u4ee5\u6781\u5927\u5730\u51cf\u5c11\u5fc5\u9700\u7684\u5b57\u7b26\u6570\u91cf\u3002\u66f4\u91cd\u8981\u7684\u662f\uff0c\u5b83\u6fc0\u52b1\u5f00\u53d1\u8005\u4e66\u5199\u66f4\u6e05\u6670\u3001\u66f4\u6613\u7ef4\u62a4\u7684\u4ee3\u7801<\/strong>\uff0c\u56e0\u4e3a\u5b83\u51cf\u5c11\u4e86\u7c7b\u578b\u7684\u5197\u957f\u58f0\u660e\uff0c\u8feb\u4f7f\u5f00\u53d1\u8005\u8d4b\u4e88\u53d8\u91cf\u4ee5\u66f4\u5177\u8868\u73b0\u529b\u7684\u540d\u79f0\u4ece\u800c\u4f7f\u4ee3\u7801\u81ea\u89e3\u91ca\u3002\u7136\u800c\uff0c\u9700\u8981\u6ce8\u610f\u7684\u662f\uff0cvar\u4e0d\u662f\u4e07\u80fd\u7684\uff0c\u5b83\u5e94\u5f53\u5728\u4e0d\u5f71\u54cd\u4ee3\u7801\u6e05\u6670\u6027\u7684\u60c5\u51b5\u4e0b\u4f7f\u7528\uff0c\u5e76\u4e14\u53ea\u80fd\u5728\u5c40\u90e8\u53d8\u91cf\u58f0\u660e\u4e2d\u4f7f\u7528\uff0c\u4e0d\u80fd\u7528\u4f5c\u6210\u5458\u53d8\u91cf\u3001\u65b9\u6cd5\u53c2\u6570\u6216\u8005\u8fd4\u56de\u7c7b\u578b\u3002<\/p>\n<\/p>\n

\u4e00\u3001var\u7684\u57fa\u672c\u5e94\u7528<\/h3>\n<\/p>\n

\u4f7f\u7528var\u6700\u57fa\u672c\u7684\u573a\u666f\u5c31\u662f\u5728\u58f0\u660e\u5c40\u90e8\u53d8\u91cf\u65f6\u66ff\u4ee3\u663e\u5f0f\u7c7b\u578b\u3002\u4f8b\u5982\uff0c\u66ff\u4ee3\u4f20\u7edf\u7684\u58f0\u660e\u65b9\u5f0f\uff1a<\/p>\n<\/p>\n

String message = "Hello Java 10";<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u4f7f\u7528var\u7684\u65b9\u5f0f\u53ef\u4ee5\u7b80\u5316\u4e3a\uff1a<\/p>\n<\/p>\n
var message = "Hello Java 10";<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0c\u7f16\u8bd1\u5668\u5c06\u6839\u636e\u5b57\u7b26\u4e32\u5b57\u9762\u91cf\u81ea\u52a8\u63a8\u65ad\u51fa\u53d8\u91cfmessage\u7684\u7c7b\u578b\u4e3aString\u3002<\/p>\n<\/p>\n
\u4e8c\u3001\u5728\u5faa\u73af\u4e2d\u7684\u5e94\u7528<\/h3>\n<\/p>\n
\u5728\u4f7f\u7528\u5faa\u73af\uff0c\u7279\u522b\u662f\u589e\u5f3a\u578bfor\u5faa\u73af\u65f6\uff0cvar\u80fd\u591f\u7b80\u5316\u4ee3\u7801\u3002\u4f20\u7edf\u7684\u5faa\u73af\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n<\/p>\n
List<String> cities = List.of("New York", "London", "Paris");<\/p>\n
for (String city : cities) {<\/p>\n
    System.out.println(city);<\/p>\n
}<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u5229\u7528var\u8fdb\u884c\u6539\u5199\uff0c\u4ee3\u7801\u53d8\u5f97\u66f4\u52a0\u7b80\u6d01\uff1a<\/p>\n<\/p>\n
var cities = List.of("New York", "London", "Paris");<\/p>\n
for (var city : cities) {<\/p>\n
    System.out.println(city);<\/p>\n
}<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u4f7f\u7528var\u540e\uff0c\u4ee3\u7801\u53d8\u5f97\u66f4\u4e3a\u7d27\u51d1\uff0c\u66f4\u91cd\u8981\u7684\u662f\uff0c\u5b83\u4fdd\u8bc1\u4e86\u4ee3\u7801\u7684\u53ef\u8bfb\u6027\u5e76\u6ca1\u6709\u56e0\u4e3a\u7c7b\u578b\u7684\u7701\u7565\u800c\u964d\u4f4e\u3002<\/p>\n<\/p>\n
\u4e09\u3001\u5728\u6d41\u5f0fAPI\u4e2d\u7684\u5e94\u7528<\/h3>\n<\/p>\n
Java\u7684Stream API\u4ee5\u53ca\u96c6\u5408\u6846\u67b6\u4e0evar\u5173\u952e\u5b57\u7ed3\u5408\u5f97\u5929\u8863\u65e0\u7f1d\u3002\u4f8b\u5982\uff0c\u5728\u4f7f\u7528\u6d41\u64cd\u4f5c\u65f6\uff1a<\/p>\n<\/p>\n
var users = getUsers().stream()<\/p>\n
                      .filter(u -> u.isActive())<\/p>\n
                      .collect(Collectors.toList());<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u8fd9\u91cc\uff0c\u4f7f\u7528var\u53ef\u4ee5\u907f\u514d\u58f0\u660e\u590d\u6742\u7684\u6cdb\u578b\u7c7b\u578b\uff0c\u540c\u65f6\u4fdd\u6301\u94fe\u5f0f\u8c03\u7528\u7684\u6d41\u7545\u6027\u548c\u6e05\u6670\u6027\u3002<\/p>\n<\/p>\n
\u56db\u3001\u6781\u7aef\u60c5\u51b5\u4e0b\u7684\u4f7f\u7528<\/h3>\n<\/p>\n
\u5c3d\u7ba1var\u80fd\u5e26\u6765\u4fbf\u5229\uff0c\u4e5f\u5e94\u5f53\u907f\u514d\u8fc7\u5ea6\u4f7f\u7528\u3002\u5728\u67d0\u4e9b\u60c5\u51b5\u4e0b\uff0c\u8fc7\u5ea6\u4f7f\u7528var\u4f1a\u5bfc\u81f4\u4ee3\u7801\u7684\u96be\u4ee5\u7406\u89e3\u3002\u8003\u8651\u5982\u4e0b\u4ee3\u7801\uff1a<\/p>\n<\/p>\n
var result = process();<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u5982\u679cprocess()<\/code>\u65b9\u6cd5\u7684\u8fd4\u56de\u7c7b\u578b\u4e0d\u662f\u4ece\u4e0a\u4e0b\u6587\u4e2d\u660e\u663e\u7684\uff0c\u90a3\u4e48\u8fd9\u6bb5\u4ee3\u7801\u53ef\u80fd\u4f1a\u9020\u6210\u9605\u8bfb\u8005\u7684\u56f0\u60d1\u3002\u56e0\u6b64\uff0c\u5728\u4f7f\u7528var\u65f6\uff0c\u5e94\u5f53\u5728\u4e0d\u635f\u5bb3\u4ee3\u7801\u660e\u786e\u6027\u7684\u524d\u63d0\u4e0b\u4f7f\u7528\u3002<\/p>\n<\/p>\n
\u4e94\u3001\u4e0e\u533f\u540d\u5185\u90e8\u7c7b\u4e00\u8d77\u4f7f\u7528<\/h3>\n<\/p>\n
\u5728\u5904\u7406\u533f\u540d\u5185\u90e8\u7c7b\u65f6\uff0cvar\u540c\u6837\u53ef\u4ee5\u51cf\u5c11\u5197\u957f\u8bed\u6cd5\u7684\u51fa\u73b0\u3002\u4f8b\u5982\uff1a<\/p>\n<\/p>\n
Runnable task = new Runnable() {<\/p>\n
    @Override<\/p>\n
    public void run() {<\/p>\n
        System.out.println("Task is running.");<\/p>\n
    }<\/p>\n
};<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u4f7f\u7528var\u7b80\u5316\u540e\uff1a<\/p>\n<\/p>\n
var task = new Runnable() {<\/p>\n
    @Override<\/p>\n
    public void run() {<\/p>\n
        System.out.println("Task is running.");<\/p>\n
    }<\/p>\n
};<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u8fd9\u79cd\u65b9\u5f0f\u7b80\u5316\u4e86\u533f\u540d\u5185\u90e8\u7c7b\u7684\u58f0\u660e\uff0c\u540c\u65f6\u4fdd\u6301\u4e86\u4ee3\u7801\u7684\u6574\u6d01\u4e0e\u53ef\u8bfb\u6027\u3002<\/p>\n<\/p>\n
\u516d\u3001\u5728try-with-resources\u4e2d\u7684\u5e94\u7528<\/h3>\n<\/p>\n
var\u4e5f\u53ef\u7528\u4e8etry-with-resources\u7ed3\u6784\u4e2d\uff0c\u4f7f\u4ee3\u7801\u66f4\u4e3a\u7b80\u6d01\uff1a<\/p>\n<\/p>\n
try (var fis = new FileInputStream("file.txt")) {<\/p>\n
    \/\/ Use the file input stream<\/p>\n
} catch (IOException e) {<\/p>\n
    \/\/ Handle exception<\/p>\n
}<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0c\u65e0\u9700\u663e\u5f0f\u58f0\u660eFileInputStream\u7c7b\u578b\uff0c\u4ece\u800c\u4f7f\u5f97\u5f02\u5e38\u5904\u7406\u4ee3\u7801\u5757\u66f4\u52a0\u7b80\u6d01\u3002<\/p>\n<\/p>\n
\u4e03\u3001var\u7684\u9650\u5236\u4e0e\u6700\u4f73\u5b9e\u8df5<\/h3>\n<\/p>\n
\u867d\u7136var\u5728\u5f88\u591a\u60c5\u51b5\u4e0b\u90fd\u53ef\u4ee5\u4f7f\u7528\uff0c\u4f46\u5b83\u4e5f\u6709\u4e00\u5b9a\u7684\u9650\u5236\u3002\u6bd4\u5982\uff0c\u5b83\u4e0d\u80fd\u7528\u4e8e\u6210\u5458\u53d8\u91cf\u7684\u58f0\u660e\u3001\u4e0d\u80fd\u7528\u5728\u65b9\u6cd5\u7684\u53c2\u6570\u4e2d\u3001\u4e0d\u80fd\u7528\u4e8e\u65b9\u6cd5\u7684\u8fd4\u56de\u7c7b\u578b\uff0c\u5e76\u4e14\u5b83\u4e0d\u652f\u6301null\u503c\u7684\u7c7b\u578b\u63a8\u65ad\u3002\u5408\u7406\u4f7f\u7528var\uff0c\u53ef\u4ee5\u9075\u5faa\u4ee5\u4e0b\u51e0\u4e2a\u6700\u4f73\u5b9e\u8df5\u539f\u5219\uff1a<\/p>\n<\/p>\n
    \n
  • \u5f53\u521d\u59cb\u503c\u8868\u8fbe\u5f0f\u63d0\u4f9b\u8db3\u591f\u7684\u4fe1\u606f\u6765\u6e05\u695a\u5730\u5224\u65ad\u53d8\u91cf\u7c7b\u578b\u65f6\uff0c\u4f7f\u7528var\u3002<\/li>\n
  • \u907f\u514d\u4f7f\u7528var\u5728\u4e00\u884c\u5185\u58f0\u660e\u591a\u4e2a\u53d8\u91cf\u3002<\/li>\n
  • \u4e0d\u8981\u4f7f\u7528var\u4f5c\u4e3a\u65b9\u6cd5\u53c2\u6570\u6216\u8fd4\u56de\u7c7b\u578b\uff0c\u56e0\u4e3a\u8fd9\u4f1a\u5f71\u54cd\u65b9\u6cd5\u7b7e\u540d\u7684\u6e05\u6670\u6027\u3002<\/li>\n
  • \u5f53\u663e\u5f0f\u7c7b\u578b\u80fd\u591f\u589e\u52a0\u4ee3\u7801\u53ef\u8bfb\u6027\u65f6\uff0c\u4e0d\u4f7f\u7528var\u3002<\/li>\n<\/ul>\n
    \u603b\u7684\u6765\u8bf4\uff0cJava 10\u7684var\u5173\u952e\u5b57<\/strong>\u65b0\u589e\u4e86\u4e00\u79cd\u7f16\u7a0b\u65b9\u5f0f\uff0c\u5b83\u8ba9\u4ee3\u7801\u66f4\u52a0\u7b80\u6d01\u800c\u5bcc\u6709\u8868\u73b0\u529b\uff0c\u63d0\u9ad8\u4e86\u5f00\u53d1\u8005\u7684\u751f\u4ea7\u6548\u7387\u3002\u7136\u800c\uff0c\u4e3a\u4e86\u4fdd\u8bc1\u4ee3\u7801\u7684\u53ef\u7ef4\u62a4\u6027\u548c\u6e05\u6670\u6027\uff0c\u5f00\u53d1\u8005\u5e94\u5f53\u5408\u7406\u5730\u4f7f\u7528var\uff0c\u907f\u514d\u8fc7\u5ea6\u4f9d\u8d56\u3002<\/p>\n<\/p>\n
    \u76f8\u5173\u95ee\u7b54FAQs\uff1a<\/strong><\/h2>\n
    Q: \u4ec0\u4e48\u662fJava 10\u7684var\u5173\u952e\u5b57\uff1f<\/strong><\/p>\n
    A: Java 10\u5f15\u5165\u4e86var\u5173\u952e\u5b57\uff0c\u5b83\u53ef\u4ee5\u7528\u6765\u63a8\u65ad\u53d8\u91cf\u7684\u7c7b\u578b\uff0c\u4f7f\u4ee3\u7801\u66f4\u7b80\u6d01\u3002\u4f7f\u7528var\u5173\u952e\u5b57\u53ef\u4ee5\u7701\u7565\u53d8\u91cf\u7684\u7c7b\u578b\u58f0\u660e\uff0c\u7f16\u8bd1\u5668\u4f1a\u6839\u636e\u8d4b\u503c\u8bed\u53e5\u63a8\u65ad\u51fa\u53d8\u91cf\u7684\u7c7b\u578b\u3002<\/p>\n
    Q: \u5728\u5f00\u53d1\u4e2d\uff0cvar\u5173\u952e\u5b57\u6709\u4ec0\u4e48\u5b9e\u9645\u5e94\u7528\uff1f<\/strong><\/p>\n
    A: var\u5173\u952e\u5b57\u53ef\u4ee5\u5728\u5f00\u53d1\u4e2d\u63d0\u9ad8\u4ee3\u7801\u7684\u53ef\u8bfb\u6027\u548c\u7f16\u5199\u6548\u7387\u3002\u5b83\u4e3b\u8981\u5e94\u7528\u4e8e\u4ee5\u4e0b\u51e0\u4e2a\u65b9\u9762\uff1a<\/p>\n
      \n
    1. \u589e\u5f3a\u7684for\u5faa\u73af\uff1a\u4f7f\u7528var\u5173\u952e\u5b57\u53ef\u4ee5\u7701\u7565\u5faa\u73af\u4e2d\u8fed\u4ee3\u53d8\u91cf\u7684\u7c7b\u578b\u58f0\u660e\uff0c\u7b80\u5316\u4ee3\u7801\u3002<\/li>\n
    2. Lambda\u8868\u8fbe\u5f0f\uff1avar\u53ef\u4ee5\u7528\u4e8e\u7701\u7565Lambda\u8868\u8fbe\u5f0f\u53c2\u6570\u7684\u7c7b\u578b\uff0c\u4f7f\u4ee3\u7801\u66f4\u52a0\u7b80\u6d01\u3002<\/li>\n
    3. \u65b9\u6cd5\u8fd4\u56de\u7c7b\u578b\uff1a\u4f7f\u7528var\u5173\u952e\u5b57\u53ef\u4ee5\u8ba9\u65b9\u6cd5\u7684\u8fd4\u56de\u7c7b\u578b\u6839\u636e\u8fd4\u56de\u503c\u7684\u7c7b\u578b\u8fdb\u884c\u63a8\u65ad\uff0c\u51cf\u5c11\u7c7b\u578b\u58f0\u660e\u7684\u5197\u4f59\u3002<\/li>\n<\/ol>\n
      Q: var\u5173\u952e\u5b57\u6709\u4ec0\u4e48\u6ce8\u610f\u4e8b\u9879\uff1f<\/strong><\/p>\n
      A: \u5728\u4f7f\u7528var\u5173\u952e\u5b57\u65f6\u9700\u8981\u6ce8\u610f\u4ee5\u4e0b\u51e0\u70b9\uff1a<\/p>\n
        \n
      1. \u53d8\u91cf\u5fc5\u987b\u8fdb\u884c\u521d\u59cb\u5316\uff1a\u7531\u4e8evar\u5173\u952e\u5b57\u662f\u901a\u8fc7\u8d4b\u503c\u8bed\u53e5\u63a8\u65ad\u53d8\u91cf\u7684\u7c7b\u578b\uff0c\u56e0\u6b64\u53d8\u91cf\u5fc5\u987b\u5728\u58f0\u660e\u65f6\u5c31\u8fdb\u884c\u521d\u59cb\u5316\u3002<\/li>\n
      2. \u4e0d\u80fd\u7528\u4e8e\u65b9\u6cd5\u53c2\u6570\u548c\u6784\u9020\u51fd\u6570\u53c2\u6570\uff1avar\u5173\u952e\u5b57\u53ea\u80fd\u7528\u4e8e\u5c40\u90e8\u53d8\u91cf\u7684\u58f0\u660e\uff0c\u4e0d\u80fd\u7528\u4e8e\u65b9\u6cd5\u53c2\u6570\u6216\u6784\u9020\u51fd\u6570\u53c2\u6570\u7684\u58f0\u660e\u3002<\/li>\n
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