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Java 12 更新
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‎README.md

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2020
- 支持脚本语言
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- JDBC4.0API
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### JDK 1.7
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### [JDK 1.7](java-7/)
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---
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- 支持try-with-resources
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- switch语句块增加String支持
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- NIO2.0包
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### **JDK 1.8**
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### [**JDK 1.8**](java-8/) - LTS
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---
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使用元空间`Metaspace`代替持久代（`PermGen space`），JVM参数使用`-XX:MetaSpaceSize`和`-XX:MaxMetaspaceSize`设置大小
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### JDK 9
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### [JDK 9](java-9/)
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---
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- [Optional更新](java-9/src/main/java/com/di1shuai/java9/optional/OptionalDemo.java)
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- JShell
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### JDK 10
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### [JDK 10](java-10/)
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---
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- 基于时间（Time-Based）的版本控制模型
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### **JDK 11**
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### [**JDK 11**](java-11/) - LTS
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---
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- 单文件java命令直接编译运行
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- [HTTP Client标准化](java-11/src/main/java/com/di1shuai/java11/http/HTTPClientDemo.java)
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### JDK 12
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### [JDK 12](java-12/)
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---
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- switch表达式
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- Shenandoah GC
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- 增强GC
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- [switch 增强](java-12/src/main/java/com/di1shuai/java12/switchdemo/SwitchDemo.java)
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- [NumberFormat - 数字的格式化](java-12/src/main/java/com/di1shuai/java12/number/NumberFormatDemo.java)
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- [Files.mismatch - 文件比较](java-12/src/main/java/com/di1shuai/java12/files/FilesDemo.java)
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- [String API更新](java-12/src/main/java/com/di1shuai/java12/string/StringDemo.java)
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- [Stream Teeing Collector](java-12/src/main/java/com/di1shuai/java12/stream/TeeingDemo.java)
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- 其他
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- 支持unicode 11（684个新字符、11个新blocks、7个新脚本）
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- JVM 常量 API （主要在新的java.lang.invoke.constant包中定义了一系列基于值的符号引用类型，能够描述每种可加载常量。）
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- Shenandoah GC（低暂停时间垃圾收集器）
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- G1 收集器提升 （可中止的混合收集集合、及时返回未使用的已分配内存）
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- 默认CDS档案
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- JMH 基准测试
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### JDK 13
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‎java-12/README.md

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### JDK 12
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---
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- [switch 增强](src/main/java/com/di1shuai/java12/switchdemo/SwitchDemo.java)
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- [NumberFormat - 数字的格式化](src/main/java/com/di1shuai/java12/number/NumberFormatDemo.java)
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- [Files.mismatch - 文件比较](src/main/java/com/di1shuai/java12/files/FilesDemo.java)
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- [String API更新](src/main/java/com/di1shuai/java12/string/StringDemo.java)
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- [Stream Teeing Collector](src/main/java/com/di1shuai/java12/stream/TeeingDemo.java)
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- 其他
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- 支持unicode 11（684个新字符、11个新blocks、7个新脚本）
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- JVM 常量 API （主要在新的java.lang.invoke.constant包中定义了一系列基于值的符号引用类型，能够描述每种可加载常量。）
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- Shenandoah GC（低暂停时间垃圾收集器）
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- G1 收集器提升 （可中止的混合收集集合、及时返回未使用的已分配内存）
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- 默认CDS档案
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- JMH 基准测试

‎java-12/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>java-versions</artifactId>
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<groupId>com.di1shuai</groupId>
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<version>1.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>java-12</artifactId>
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<properties>
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<maven.compiler.source>14</maven.compiler.source>
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<maven.compiler.target>14</maven.compiler.target>
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</properties>
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<dependencies>
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<dependency>
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<groupId>org.projectlombok</groupId>
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<artifactId>lombok</artifactId>
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<scope>provided</scope>
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</dependency>
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</dependencies>
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</project>

‎java-12/src/main/java/com/di1shuai/java12/Student.java

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package com.di1shuai.java12;
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import lombok.AllArgsConstructor;
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import lombok.Data;
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/**
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* @author Shea
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* @date 2021-01-22
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* @description
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*/
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@Data
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@AllArgsConstructor
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public class Student {
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private String name;
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private Integer age;
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}

‎java-12/src/main/java/com/di1shuai/java12/files/FilesDemo.java

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package com.di1shuai.java12.files;
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import java.io.IOException;
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import java.nio.file.Files;
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import java.nio.file.Path;
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import java.nio.file.Paths;
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/**
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* @author Shea
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* @date 2021-01-22
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* @description 文件比较 mismatch 返回第一个不匹配的位置，如果都匹配就返回-1L
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*/
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public class FilesDemo {
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public static void main(String[] args) {
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Path path1 = Paths.get("/Users/shuai/Documents/GitRepo/mine/language/java-versions/java-12/src/main/java/com/di1shuai/java12/files/FilesDemo.java");
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Path path2 = Paths.get("/Users/shuai/Documents/GitRepo/mine/language/java-versions/java-12/src/main/java/com/di1shuai/java12/files/FilesDemo.java");
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try {
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long fileMismatch = Files.mismatch(path1, path2);
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System.out.println(fileMismatch);
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} catch (IOException e) {
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e.printStackTrace();
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}
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}
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}

‎java-12/src/main/java/com/di1shuai/java12/number/NumberFormatDemo.java

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package com.di1shuai.java12.number;
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import java.text.NumberFormat;
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import java.util.Locale;
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/**
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* @author Shea
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* @date 2021-01-22
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* @description
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*/
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public class NumberFormatDemo {
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public static void main(String[] args) {
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long number = 100000;
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NumberFormat nfChina = NumberFormat.getCompactNumberInstance(Locale.CHINA, NumberFormat.Style.SHORT);
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System.out.println(nfChina.format(number));
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//10万
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NumberFormat nfUK = NumberFormat.getCompactNumberInstance(Locale.UK, NumberFormat.Style.SHORT);
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System.out.println(nfUK.format(number));
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//100K
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}
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}

‎java-12/src/main/java/com/di1shuai/java12/stream/TeeingDemo.java

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package com.di1shuai.java12.stream;
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import com.di1shuai.java12.Student;
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import java.util.Arrays;
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import java.util.Collections;
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import java.util.List;
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import java.util.stream.Collectors;
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/**
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* @author Shea
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* @date 2021-01-22
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* @description T 操作 合并两个
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*/
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public class TeeingDemo {
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public static void main(String[] args) {
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List<Student> students = Arrays.asList(
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new Student("shea", 28),
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new Student("abel", 25),
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new Student("sean", 40)
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);
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String collect = students.stream().collect(Collectors.teeing(
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Collectors.averagingInt(Student::getAge),
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Collectors.summingInt(Student::getAge),
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(avgAge, sumAge) -> avgAge + " : " + sumAge
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));
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System.out.println(collect);
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}
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}

‎java-12/src/main/java/com/di1shuai/java12/string/StringDemo.java

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package com.di1shuai.java12.string;
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import java.util.List;
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/**
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* @author Shea
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* @date 2021-01-22
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* @description API更新
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* <p>
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* transform 字符串转换，可以配合函数式接口Function一起使用
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* indent 缩进，每行开头增加空格space和移除空格
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*/
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public class StringDemo {
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public static void main(String[] args) {
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//transform
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List.of(" Hello ", " Hi ").forEach(
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s -> {
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String newStr = s.transform(String::strip)
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.transform(e -> e + " Java 12");
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System.out.println(newStr);
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});
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//indent
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String result = "Hello\nJava\n12\n".indent(3);
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System.out.println(result);
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}
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}

‎java-12/src/main/java/com/di1shuai/java12/switchdemo/SwitchDemo.java

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package com.di1shuai.java12.switchdemo;
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/**
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* @author Shea
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* @date 2021-01-22
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* @description Switch 增强 (预览)
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* case 多个 -> xxx;
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*
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*/
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public class SwitchDemo {
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enum DAY {
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MONDAY,
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TUESDAY,
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WEDNESDAY,
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THURSDAY,
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FRIDAY,
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SATURDAY,
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SUNDAY
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}
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enum TODAY {
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WEEKEND_DAY,
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WORKING_DAY
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}
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public static void main(String[] args) {
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DAY day = DAY.MONDAY;
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TODAY toDay = whatIsTodayBefore12(day);
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System.out.println(toDay);
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toDay = whatIsToday12(day);
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System.out.println(toDay);
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}
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private static TODAY whatIsTodayBefore12(DAY day) {
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// Before 12
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TODAY today;
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switch (day) {
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case MONDAY:
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case TUESDAY:
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case WEDNESDAY:
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case THURSDAY:
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case FRIDAY:
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today = TODAY.WORKING_DAY;
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break;
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case SATURDAY:
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case SUNDAY:
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today = TODAY.WEEKEND_DAY;
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break;
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default:
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throw new RuntimeException("N/A");
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}
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return today;
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}
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private static TODAY whatIsToday12(DAY day) {
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// 12
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TODAY today;
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switch (day) {
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case MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY -> today = TODAY.WORKING_DAY;
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case SATURDAY, SUNDAY -> today = TODAY.WEEKEND_DAY;
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default -> throw new IllegalArgumentException("Invalid day");
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}
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return today;
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}
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}

‎pom.xml

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<module>java-9</module>
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<module>java-7</module>
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<module>java-10</module>
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<module>java-12</module>
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</modules>
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<dependencyManagement>

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