JDK 13新特性详解

学习笔记 : 详解JDK 13中的新特性

简介

JDK 13 is the open-source reference implementation of version 13 of the Java SE Platform as specified by by JSR 388 in the Java Community Process. JDK 13 reached General Availability on 17 September 2019. Production-ready binaries under the GPL are available from Oracle; binaries from other vendors will follow shortly. The features and schedule of this release were proposed and tracked via the JEP Process, as amended by the JEP 2.0 proposal. The release was produced using the JDK Release Process (JEP 3).

特性

350: Dynamic CDS Archives
351: ZGC: Uncommit Unused Memory
353: Reimplement the Legacy Socket API
354: Switch Expressions (Preview)
355: Text Blocks (Preview)

时间表

2019/06/13 Rampdown Phase One (fork from main line)
2019/07/18 Rampdown Phase Two
2019/08/08 Initial Release Candidate
2019/08/22 Final Release Candidate
2019/09/17 General Availability

Switch Expressions 特性演示

 /*
JDK12之前版本的写法:许多break使它不必要地冗长,如果忘记写break,则会产生意料之外的结果或者异常,所以针对于此jdk12在这里进行了优化升级
*/
switch (score) {
    case 60:
        System.out.println("及格");
        break;
    case 80:
        System.out.println("良好");
        break;
    case 90:
        System.out.println("优秀");
        break;
    default:
        System.out.println("default");
        break;
}

/*
JDK12新特性写法:我们建议引入一种新形式的开关标签,写成"case L ->"表示如果标签匹配,则只执行标签右侧的代码
*/
switch (score) {
    case 60 -> System.out.println("及格");
    case 80 -> System.out.println("良好");
    case 90 -> System.out.println("优秀");
    default -> System.out.println("default");
}

/*
JDK13新特性写法:优化JDK12中的switch语法新特性,使其更加简洁~
*/
System.out.println(
        switch (score) {
            case 60 -> "及格";
            case 80 -> "良好";
            case 90 -> "优秀";
            default -> "default";
        }
);

Text Blocks 特性演示

//解释:左边的文本块相当于右边的字符串文字
/*
"""
line1
line2   ------>>>   "line 1\nline 2\nline 3\n"
line3
"""
*/


/*
HTML 示例程序
*/
//JDK13版本前的写法
String html = "<html>\n" +
        "    <body>\n" +
        "        <p>Hello, world</p>\n" +
        "    </body>\n" +
        "</html>\n";

//JDK13语法新特性的写法
String html2 =
        """
            <html>
                <body>
                    <p>Hello, world</p>
                </body>
            </html>
        """;


/*
SQL 示例程序
*/
 //JDK13版本前的写法
String query = "SELECT `EMP_ID`, `LAST_NAME` FROM `EMPLOYEE_TB`\n" +
        "WHERE `CITY` = 'INDIANAPOLIS'\n" +
        "ORDER BY `EMP_ID`, `LAST_NAME`;\n";

//JDK13新特性的写法
String query2 =
        """
        SELECT `EMP_ID`, `LAST_NAME` FROM `EMPLOYEE_TB`
        WHERE `CITY` = 'INDIANAPOLIS'
        ORDER BY `EMP_ID`, `LAST_NAME`;
        """;