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为什么要写这篇文章

经过了若干年的发展，Java逐步从 java8 升级为 java11 ， java17 。

让我们对比学习一下最新一版的LTS版本和 java8 比起来让代码简化了多少。

1. 文本块（Text Blocks）。

这个写法有些类似于 javascript、 Lua等脚本语言。方便识别html、json等格式复杂的字符串。

public class StringTest {public static void main(String[] args) throws Exception {// 传统写法String json ="{\n" +"    \"key\":\"a\",\n" +"    \"value\":\"b\"\n" +"}";// 优化后写法String json2 = """{"key":"a","value":"b"}""";// 返回为 trueSystem.out.println(json == json2);}
}

1. 本地变量类型推断（Local Variable Type Inference）

这一点也是在一些脚本语言中常见的，类似于 var 表示变量，val 表示常量。

public static void main(String[] args) throws Exception {//集合// immutable map buildvar map = Map.of("cat", "猫","dog", "狗","fish", "鱼");// immutable set buildvar set = Set.of("1", "2", "3");// immutable list buildvar list = List.of(1, 2, 3, 4, 5);// 循环语句for (var i = 1; i < list.size(); i++) {System.out.println(i);}for (var i : list) {System.out.println(i);}// 异常try (var in = new ByteArrayInputStream("123".getBytes())) {System.out.println(new String(in.readAllBytes(), "utf-8"));} catch (Exception e) {System.out.println(e);}// lambda 表达式 意思相同BiFunction<Integer, Integer, Integer> biFunction = (a, b) -> a + b;BiFunction<Integer, Integer, Integer> biFunction2 = (var a, var b) -> a + b;}

1. switch

public static void main(String[] args) throws Exception {var eating = Eating.BREAKFAST;String eatingZnString = "";// 传统写法switch (eating) {case BREAKFAST:case LUNCH:eatingZnString = "早午饭";break;case DINNER:eatingZnString = "晚饭";break;default:throw new Exception();}System.out.println(eatingZnString);// 优化后写法System.out.println(switch (eating) {case BREAKFAST,LUNCH -> "早午饭";case DINNER -> "晚饭";default -> throw new Exception();});}

1. instance of 操作符的模式匹配(Pattern Matching for the instanceof Operator)

interface Animal {}class Cat implements Animal {public void mew() {System.out.println("喵");}
}class Dog implements Animal {public void woof() {System.out.println("汪");}
}public class Test {// 传统写法public static void sounds(Animal animal) {if (animal instanceof Cat) {Cat cat = (Cat) animal;cat.mew();} else if (animal instanceof Dog) {Dog dog = (Dog) animal;dog.woof();} else {throw new IllegalArgumentException("没有这种动物的叫声");}}// 优化写法public static void betterSounds(Animal animal) {if (animal instanceof Cat cat) {cat.mew();} else if (animal instanceof Dog dog) {dog.woof();} else {throw new IllegalArgumentException("没有这种动物的叫声");}}
}

1. record 类

// 传统类
public record People(String name, int age) {public People(String name, int age) {this.name = name;this.age = age;}public String name() {return this.name;}public int age() {return this.age;}public boolean equals(People people) {...}public int hashCode() {...}public String toString() {...}
}// 优化后的类
public record People (String name, int age){ }// 更多用法
public record People (String name, int age){// 静态字段static int teenageAge;// 静态初始化static {teenageAge = 17;}// 静态方法public static People buildTeenage(String name) {return new People(name , teenageAge);}// 优化后的构造方法public People {if (age < 0) {throw new IllegalArgumentException("年龄不能小于0");}}
}