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Commit e85e3c9

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coderbruiscoderbruis
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lambda map
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‎JdkLearn/src/main/java/com/learnjava/lambda/LambdaComparatorDemo.java‎

Copy file name to clipboardExpand all lines: JdkLearn/src/main/java/com/learnjava/lambda/LambdaComparatorDemo.java
+27-13Lines changed: 27 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -2,16 +2,36 @@
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import lombok.AllArgsConstructor;
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import lombok.Data;
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import sun.java2d.pipe.SpanShapeRenderer;
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import java.text.SimpleDateFormat;
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import java.util.Arrays;
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import java.util.Comparator;
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import java.util.Date;
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import java.util.List;
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import java.util.function.Predicate;
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import java.util.stream.Stream;
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public class LambdaComparatorDemo {
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public static String[] arrays = {"Milan", "london", "San Francisco", "Tokyo", "New Delhi"};
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public static List<Employee> employees;
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static {
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Employee e1 = new Employee(1,23,"M","Rick","Beethovan", "2021-04-01");
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Employee e2 = new Employee(2,13,"F","Martina","Hengis", "2021-04-02");
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Employee e3 = new Employee(3,43,"M","Ricky","Martin","2021-04-03" );
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Employee e4 = new Employee(4,26,"M","Jon","Lowman", "2021-04-04");
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Employee e5 = new Employee(5,19,"F","Cristine","Maria", "2021-04-05");
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Employee e6 = new Employee(6,15,"M","David","Feezor", "2021-04-06");
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Employee e7 = new Employee(7,68,"F","Melissa","Roy", "2021-04-07");
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Employee e8 = new Employee(8,79,"M","Alex","Gussin", "2021-04-08");
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Employee e9 = new Employee(9,15,"F","Neetu","Singh", "2021-04-09");
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Employee e10 = new Employee(10,45,"M","Naveen","Jain", "2021-04-10");
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employees = Arrays.asList(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10);
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}
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public static void main(String[] args) {
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// test01();
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// test02();
@@ -60,19 +80,6 @@ public static void test02() {
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* 对对象进行排序
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*/
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public static void test03() {
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Employee e1 = new Employee(1,23,"M","Rick","Beethovan");
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Employee e2 = new Employee(2,13,"F","Martina","Hengis");
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Employee e3 = new Employee(3,43,"M","Ricky","Martin");
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Employee e4 = new Employee(4,26,"M","Jon","Lowman");
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Employee e5 = new Employee(5,19,"F","Cristine","Maria");
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Employee e6 = new Employee(6,15,"M","David","Feezor");
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Employee e7 = new Employee(7,68,"F","Melissa","Roy");
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Employee e8 = new Employee(8,79,"M","Alex","Gussin");
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Employee e9 = new Employee(9,15,"F","Neetu","Singh");
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Employee e10 = new Employee(10,45,"M","Naveen","Jain");
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List<Employee> employees = Arrays.asList(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10);
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// 根据employee的年龄进行自然排序
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employees.sort(Comparator.comparing(Employee::getAge));
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employees.forEach(System.out::println);
@@ -136,6 +143,7 @@ public static class Employee {
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private String gender;
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private String firstName;
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private String lastName;
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private String date;
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@Override
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public String toString() {
@@ -145,7 +153,13 @@ public String toString() {
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", gender='" + gender + '\'' +
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", firstName='" + firstName + '\'' +
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", lastName='" + lastName + '\'' +
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", date='" + date + '\'' +
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'}';
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}
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// 年龄大于70的谓语
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static Predicate<Employee> ageGreaterThan70 = e -> e.getAge() > 70;
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static Predicate<Employee> ageLessThan18 = e -> e.getAge() < 18;
150164
}
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}
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‎JdkLearn/src/main/java/com/learnjava/lambda/LambdaMapDemo.java‎

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+42Lines changed: 42 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,42 @@
1+
package com.learnjava.lambda;
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import java.text.SimpleDateFormat;
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import java.util.Date;
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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 bruis
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* 操作Map
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*/
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public class LambdaMapDemo {
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public static SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
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public static void main(String[] args) {
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test01();
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}
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/**
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* 需求，将employee集合中的元素根据date进行排序
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*/
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public static void test01() {
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List<LambdaComparatorDemo.Employee> sortedByDate = LambdaComparatorDemo.employees
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.stream()
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.sorted((a, b) -> {
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int result;
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try {
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result = getDate(b.getDate()).compareTo(getDate(a.getDate()));
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} catch (Exception e) {
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result = 0;
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}
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return result;
34+
})
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.collect(Collectors.toList());
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System.out.println(sortedByDate);
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}
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public static Date getDate(String date) throws Exception {
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return format.parse(date);
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}
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}
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‎JdkLearn/src/main/java/com/learnjava/lambda/LambdaReduceDemo.java‎

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+104Lines changed: 104 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,104 @@
1+
package com.learnjava.lambda;
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import java.util.Arrays;
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import java.util.List;
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import java.util.stream.Stream;
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/**
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* @author bruis
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* 累加器
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*/
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public class LambdaReduceDemo {
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public static void main(String[] args) {
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// test01();
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// test02();
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test03();
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}
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/**
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* 对整形进行操作
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*/
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public static void test01() {
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List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
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Integer reduce = numbers
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.stream()
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.reduce(0, LambdaReduceDemo::mySum);
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// .reduce(0, Integer::sum);
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// .reduce(0, (total, element) -> total + element);
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System.out.println(reduce);
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}
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/**
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* 对字符串进行操作
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*/
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public static void test02() {
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List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
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String reduce = letters
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.stream()
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.reduce("", String::concat);
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// .reduce("", (totol, element) -> totol.concat(element));
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System.out.println(reduce);
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}
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/**
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* 操作Employee集合元素，将所有员工的年龄通过reduce累加起来
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*
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* U identity, BiFunction<U, ? super T, U> accumulator, BinaryOperator<U> combiner
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* reduce的三个参数：
49+
* 1）初始值；
50+
* 2）累加器（可自己实现逻辑）
51+
* 3) 合并器（parallelStream模式时的合并）
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*
53+
*/
54+
public static void test03() {
55+
// 将Employee集合元素转化为Integer集合元素（流）
56+
// map的操作就是将a类型元素转化为b类型元素
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Stream<Integer> integerStream = LambdaComparatorDemo
58+
.employees
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.stream()
60+
.map(LambdaComparatorDemo.Employee::getAge);
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// 求所有员工的年龄
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Integer totalAge = integerStream.reduce(0, Integer::sum);
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System.out.println(totalAge);
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// 数据量大的话，可以用并行计算
67+
// 先讲员工集合转化为“并行流”
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Stream<Integer> parallelStream = LambdaComparatorDemo
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.employees
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.parallelStream()
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.map(LambdaComparatorDemo.Employee::getAge);
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// 相比于普通的单个流，parallelStream多了个合并器，将多个CPU计算的结果再合并到同一个流
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Integer reduce = parallelStream.reduce(0, Integer::sum, Integer::sum);
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System.out.println(reduce);
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77+
// 可以不用map将employee转化为Integer对象，可以直接reduce操作，最后通过Integer::sum这个合并器来将结果合并为Integer类型
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Integer total = LambdaComparatorDemo
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.employees
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.stream()
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.reduce(0, (subTotal, emp) -> subTotal + emp.getAge(), Integer::sum);
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System.out.println(total);
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Integer total2 = LambdaComparatorDemo
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.employees
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.stream()
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.reduce(0, LambdaReduceDemo::mySum2, Integer::sum);
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System.out.println(total2);
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}
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/**
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* 可作为BiFunction，传入到reduce作为入参
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* @param a
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* @param b
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* @return
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*/
97+
public static Integer mySum(int a, int b) {
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return a + b;
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}
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public static Integer mySum2(int a, LambdaComparatorDemo.Employee employee) {
102+
return a + employee.getAge();
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}
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}
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‎JdkLearn/src/main/java/com/learnjava/lambda/StreamMatchDemo.java‎

Copy file name to clipboard
+49Lines changed: 49 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,49 @@
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package com.learnjava.lambda;
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import java.util.Optional;
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/**
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* @author bruis
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*/
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public class StreamMatchDemo {
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public static void main(String[] args) {
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// test01();
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test02();
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}
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/**
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* 判断是否有年龄大于70的员工
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*/
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public static void test01() {
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boolean isExistAgeThan70 = LambdaComparatorDemo.employees
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.stream()
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// 使用了Employee的谓语语句（这种写法方便复用）
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.anyMatch(LambdaComparatorDemo.Employee.ageGreaterThan70);
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// .anyMatch(e -> e.getAge() > 70);
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System.out.println(isExistAgeThan70);
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boolean isExistAgeLessThan18 = LambdaComparatorDemo.employees
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.stream()
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.noneMatch(LambdaComparatorDemo.Employee.ageLessThan18);
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System.out.println(isExistAgeLessThan18);
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}
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/**
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* 元素查找与Optional
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*/
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public static void test02() {
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Optional<LambdaComparatorDemo.Employee> employeeOptional = LambdaComparatorDemo.employees
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.stream()
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.filter(e -> e.getAge() > 400)
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.findFirst();
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// Optional#get 会报空
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// System.out.println(employeeOptional.get());
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LambdaComparatorDemo.Employee employee = employeeOptional.orElse(null);
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System.out.println(employee == null);
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}
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}

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