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# Default ignored files |
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/shelf/ |
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/workspace.xml |
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# Datasource local storage ignored files |
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/../../../../:\java project\mergedemo\.idea/dataSources/ |
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/dataSources.local.xml |
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# Editor-based HTTP Client requests |
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/httpRequests/ |
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<?xml version="1.0" encoding="UTF-8"?> |
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<project version="4"> |
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<component name="CompilerConfiguration"> |
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<annotationProcessing> |
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<profile default="true" name="Default" enabled="true" /> |
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<profile name="Maven default annotation processors profile" enabled="true"> |
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<sourceOutputDir name="target/generated-sources/annotations" /> |
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<sourceTestOutputDir name="target/generated-test-sources/test-annotations" /> |
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<outputRelativeToContentRoot value="true" /> |
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<module name="mergedemo" /> |
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</profile> |
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</annotationProcessing> |
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</component> |
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</project> |
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<?xml version="1.0" encoding="UTF-8"?> |
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<project version="4"> |
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<component name="RemoteRepositoriesConfiguration"> |
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<remote-repository> |
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<option name="id" value="central" /> |
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<option name="name" value="Central Repository" /> |
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<option name="url" value="https://repo.maven.apache.org/maven2" /> |
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</remote-repository> |
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<remote-repository> |
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<option name="id" value="central" /> |
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<option name="name" value="Maven Central repository" /> |
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<option name="url" value="https://repo1.maven.org/maven2" /> |
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</remote-repository> |
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<remote-repository> |
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<option name="id" value="jboss.community" /> |
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<option name="name" value="JBoss Community repository" /> |
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<option name="url" value="https://repository.jboss.org/nexus/content/repositories/public/" /> |
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</remote-repository> |
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</component> |
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</project> |
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<?xml version="1.0" encoding="UTF-8"?> |
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<project version="4"> |
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<component name="ExternalStorageConfigurationManager" enabled="true" /> |
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<component name="MavenProjectsManager"> |
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<option name="originalFiles"> |
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<list> |
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<option value="$PROJECT_DIR$/pom.xml" /> |
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</list> |
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</option> |
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</component> |
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<component name="ProjectRootManager" version="2" languageLevel="JDK_1_8" project-jdk-name="1.8" project-jdk-type="JavaSDK"> |
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<output url="file://$PROJECT_DIR$/out" /> |
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</component> |
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</project> |
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<?xml version="1.0" encoding="UTF-8"?> |
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<module type="JAVA_MODULE" version="4" /> |
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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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<modelVersion>4.0.0</modelVersion> |
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|
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<groupId>com.woniu</groupId> |
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<artifactId>mergedemo</artifactId> |
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<version>1.0-SNAPSHOT</version> |
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|
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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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<version>1.18.24</version> |
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</dependency> |
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</dependencies> |
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|
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|
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</project> |
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package com.woniu.mergedemo; |
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|
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|
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import java.util.*; |
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|
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/** |
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* Java 8 中 Map的一个骚操作!好用到爆!! |
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* |
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* 假设我们有这么一段业务逻辑, |
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* 我有一个学生成绩对象的列表, |
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* 对象包含学生姓名、科目、科目分数三个属性, |
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* 要求求得每个学生的总成绩。 |
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*/ |
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public class MainTest { |
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|
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public static void main(String[] args) { |
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List<StudentScore> studentScoreList = Arrays.asList( |
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new StudentScore("张三", "语文", 70), |
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new StudentScore("张三", "数学", 70), |
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new StudentScore("张三", "英语", 65), |
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new StudentScore("李四", "语文", 68), |
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new StudentScore("李四", "数学", 70), |
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new StudentScore("李四", "英语", 90), |
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new StudentScore("王五", "语文", 80), |
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new StudentScore("王五", "数学", 85), |
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new StudentScore("王五", "英语", 70) |
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); |
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|
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Map<String, Integer> studentScoreMap = new HashMap<>(); |
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studentScoreList.forEach(studentScore -> { |
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if (studentScoreMap.containsKey(studentScore.getStuName())) { |
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studentScoreMap.put(studentScore.getStuName(), studentScoreMap.get(studentScore.getStuName()) + studentScore.getScore()); |
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} else { |
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studentScoreMap.put(studentScore.getStuName(), studentScore.getScore()); |
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} |
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}); |
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|
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Map<String, Integer> studentScoreMap2 = new HashMap<>(); |
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studentScoreList.forEach(studentScore -> studentScoreMap2.merge( |
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studentScore.getStuName(), |
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studentScore.getScore(), |
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(oldValue, newValue) -> oldValue + newValue)); |
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//merge() 方法会先判断指定的 key 是否存在,如果不存在,则添加键值对到 hashMap 中。
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|
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} |
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|
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|
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|
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} |
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package com.woniu.mergedemo; |
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|
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import lombok.AllArgsConstructor; |
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import lombok.Data; |
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@Data |
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@AllArgsConstructor |
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public class StudentScore { |
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private String stuName; |
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private String subject; |
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private int score; |
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} |
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