记录一些JDK的新特性~持续更新

1、record快速定义类

@Test
    public void testRecord() {

        /**
         * JDK16新特性
         *
         * @param start
         * @param end
         */
        record qiu(int start, int end) {
            int sum() {
                return qiu.this.start + qiu.this.end;
            }
        }
        qiu q1 = new qiu(1, 2);
        System.out.println("q1 = " + q1);
        qiu q2 = new qiu(3, 4);
        System.out.println("q2 = " + q2);
        System.out.println(q1.equals(q2));
        // 调用方法
        System.out.println("q1.sum() = " + q1.sum());
        System.out.println("q2.sum() = " + q2.sum());
    }

2、字符串的新方法

    /**
     * isBlank()：如果字符串为空或字符串仅包含空格（包括制表符），则返回 true。注意与isEmpty() 不同，isEmpty()仅在长度为 0 时返回 true。
     * lines()：将字符串拆分为字符串流，每个字符串包含一行。
     * strip() ： 分别从开头和结尾；
     * stripLeading()/stripTrailing()仅开始和仅结束删除空格。
     * repeat(int times)：返回一个字符串，该字符串采用原始字符串并按指定的次数重复该字符串。
     * readString()：允许从文件路径直接读取到字符串。
     * writeString(Path path)：将字符串直接写入指定路径处的文件。
     * indent(int level)：缩进字符串的指定量。负值只会影响前导空格。
     * transform(Function f)：将给定的 lambda 应用于字符串。
     */
    @SneakyThrows
    @Test
    public void testNewStringMethod() {
        String str1 = "";
        System.out.println(str1.isBlank()); // true
        System.out.println(str1.isEmpty()); // true
        str1 = "   ";
        System.out.println(str1.isBlank()); // true
        System.out.println(str1.isEmpty()); // false
        str1 = "\r";
        System.out.println(str1.isBlank()); // true
        System.out.println(str1.isEmpty()); // false
        str1 = "\r\n";
        System.out.println(str1.isBlank()); // true
        System.out.println(str1.isEmpty()); // false

        System.out.println("============================================================");

        String str2 = "hello qiu \r\n qiu 我的最爱 JDK17 \n\r!\r";
        Stream<String> stream = str2.lines();
        stream.forEach(System.out::println);

        System.out.println("============================================================");

        String strip = str2.strip();
        System.out.println("strip = " + strip);
        System.out.println("str2.stripTrailing() = " + str2.stripTrailing());
        System.out.println("str2.stripIndent() = " + str2.stripIndent());
        System.out.println("str2.stripLeading() = " + str2.stripLeading());

        System.out.println("============================================================");

        String str3 = "qiu";
        String repeat = str3.repeat(3);
        System.out.println("repeat = " + repeat);

        System.out.println("============================================================");
        String path = "F:\\a.txt";
        Path of = Path.of(path);
        String string = Files.readString(of);
        System.out.println("readString = " + string);

        List<String> asList = Arrays.asList("1", "2", "3", "4", "5");
        // Files.write(Paths.get("./test"),list, StandardOpenOption.APPEND);
        Files.write(Paths.get("F:\\a.txt"), asList, StandardCharsets.UTF_8, StandardOpenOption.APPEND);


        Path writeString = Files.writeString(of, "writeString", StandardOpenOption.APPEND);
        System.out.println("writeString = " + writeString);
        System.out.println("============================================================");

        String path3 = "F:\\a.txt";
        System.out.println(path3.indent(2));
    }

3、switch优雅的写法

// 以前的写法
String result = "";
int caseNum = 4;
switch (caseNum){
	case 1 :
		result = "zs";
		break;
	case  2 :
		result = "ls";
		break;
	case 3 :
		result = "ww";
		break;
	default:
		result = "qiuqiu";
}
System.out.println("result = " + result);

// 现在的写法
result = switch (caseNum) {
	case 1 -> "张三";
	case 2 -> "李四";
	case 3 -> "王五";
	default -> "秋秋";
};
System.out.println("result = " + result);