马晓=>JAVA培训List集合

src/main/java/com/exercise/ninth/ExerciseFifth.java

+package com.exercise.ninth;
+
+import java.util.*;
+
+/**
+ * 有如下Student 对象，包含三个属性姓名、年龄、分数，班号，
+ *  　private String name;
+ *     private int age;
+ *     private int score;
+ *     private String classNum;
+ * 其中，classNum 表示学生的班号，例如“class05”。 创建集合并完成下列要求：
+ * 1） 计算所有学生的平均年龄
+ * 2） 计算各个班级的平均分
+ *
+ * 姓名     年龄     分数    班号
+ * Tom     18     100   class05
+ * Jerry   22     70    class04
+ * Owen    25     90    class05
+ * Jim     30     80    class05
+ * Steve   28     66    class06
+ * Kevin   24     100   class04
+ *
+ * @author elliot
+ */
+public class ExerciseFifth {
+    public static void main(String[] args) {
+        List<Student1> student1s = new ArrayList<>();
+        student1s.add(new Student1("Tom", 18, 100, Class.class05));
+        student1s.add(new Student1("Jerry", 22, 70, Class.class04));
+        student1s.add(new Student1("Owen", 25, 90, Class.class05));
+        student1s.add(new Student1("Jim", 30, 80, Class.class05));
+        student1s.add(new Student1("Steve", 28, 66, Class.class06));
+        student1s.add(new Student1("Kevin", 24, 100, Class.class04));
+        Iterator<Student1> student1Iterator = student1s.iterator();
+
+        double totalAge = 0;
+        Map<Class, Integer> classN = new HashMap<>();
+        Map<Class, Double> classScore = new HashMap<>();
+
+        System.out.println("所有学生信息");
+        while (student1Iterator.hasNext()) {
+            Student1 student1 = student1Iterator.next();
+            totalAge += student1.getAge();
+            classScore.put(student1.getClassNum(), classScore.getOrDefault(student1.getClassNum(), 0.0)
+                    + student1.getScore());
+            classN.put(student1.getClassNum(), classN.getOrDefault(student1.getClassNum(), 0) + 1);
+            System.out.println(student1);
+        }
+
+        // 平均年龄
+        System.out.printf("学生平均年龄 %.2f%n", totalAge / student1s.size());
+
+        // 班级平均分
+        for (Class cls: classScore.keySet()){
+            double avg = classScore.getOrDefault(cls, 0.0) / classN.getOrDefault(cls, 0);
+            System.out.printf("班级 %s 的平均分为 %.2f%n", cls, avg);
+        }
+    }
+}
+
+enum Class {
+    class04, class05, class06
+}
+
+class Student1 {
+    private String name;
+    private int age;
+    private int score;
+    private Class classNum;
+
+    public Student1(String name, int age, int score, Class classNum) {
+        this.name = name;
+        this.age = age;
+        this.score = score;
+        this.classNum = classNum;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public int getScore() {
+        return score;
+    }
+
+    public Class getClassNum() {
+        return classNum;
+    }
+
+    @Override
+    public String toString() {
+        return String.format("姓名 %s 年龄 %d 分数 %d 班号 %s", name, age, score, classNum);
+    }
+}

src/main/java/com/exercise/ninth/ExerciseFirst.java

+package com.exercise.ninth;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 马晓=>JAVA培训List集合
+ * 定义一个集合，集合中元素及元素出现的次数为 "a":2,“b”:2,“c”:1,“xxx”:0
+ * @author elliot
+ */
+public class ExerciseFirst {
+    public static void main(String[] args) {
+        List<String> stringLists = new ArrayList<>();
+        stringLists.add("a");
+        stringLists.add("b");
+        stringLists.add("a");
+        stringLists.add("b");
+        stringLists.add("c");
+        System.out.println(stringLists);
+    }
+}

src/main/java/com/exercise/ninth/ExerciseFourth.java

+package com.exercise.ninth;
+
+import java.util.*;
+
+/**
+ * 创建一个List，在List 中增加三个工人Worker，基本信息如下：
+ * 姓名     年龄   工资
+ * zhang3   18   3000
+ * li4      25   3500
+ * wang5    22   3200
+ * 2) 在li4 之前插入一个工人，信息为：姓名：zhao6，年龄：24，工资：3300
+ * 3) 删除wang5 的信息
+ * 4) 利用for 循环遍历，打印List 中所有工人的信息
+ * @author elliot
+ */
+public class ExerciseFourth {
+    public static void main(String[] args) {
+        List<Worker> workerList = new ArrayList<>();
+        workerList.add(new Worker("zhang3", 18, 300000L));
+        workerList.add(new Worker("li4", 25, 350000L));
+        workerList.add(new Worker("wang5", 22, 320000L));
+        System.out.println(workerList);
+
+        workerList.add(1, new Worker("zhao6", 24, 330000L));
+        workerList.remove(3);
+        Iterator<Worker> iterator = workerList.iterator();
+
+        while(iterator.hasNext()) {
+            System.out.println(iterator.next());
+        }
+    }
+
+}
+
+class Worker {
+    private String name;
+    private int age;
+    private long salary;
+
+    public Worker(String name, int age, long salary) {
+        this.name = name;
+        this.age = age;
+        this.salary = salary;
+    }
+
+    @Override
+    public String toString() {
+        return String.format("姓名 %s 年龄 %d 工资 %.2f", name, age, salary / 100.00);
+    }
+}

src/main/java/com/exercise/ninth/ExerciseSecond.java

+package com.exercise.ninth;
+
+import java.util.*;
+
+/**
+ * 定义一个集合， 要求：
+ * 1）元素及对应元素出现次数分别为 "a":2,“b”:3“c”:1,
+ * 2）删除重复的元素
+ * @author elliot
+ */
+public class ExerciseSecond {
+    public static void main(String[] args) {
+        List<String> stringLists = new ArrayList<>();
+        stringLists.add("a");
+        stringLists.add("b");
+        stringLists.add("a");
+        stringLists.add("b");
+        stringLists.add("b");
+        stringLists.add("c");
+        System.out.println(stringLists);
+        Iterator<String> iterator = stringLists.iterator();
+        Set<String> mySet = new HashSet<>();
+        while (iterator.hasNext()) {
+            if (!mySet.add(iterator.next())) {
+                iterator.remove();
+            }
+        }
+        System.out.println(stringLists);
+    }
+}

src/main/java/com/exercise/ninth/ExerciseThird.java

+package com.exercise.ninth;
+
+import java.util.*;
+
+/**
+ * 定义一个学生类Student，包含三个属性姓名name、年龄age、性别gender，创建三个学生对象存入ArrayList集合中。
+ * 姓名   年龄  性别
+ * 张三   20   男
+ * 李希   39   男
+ * 小七   18   女
+ *   1）：遍历集合遍历输出。
+ *   2）：求出年龄最大的学生，然后将该对象的姓名变为：葫芦娃。
+ * @author elliot
+ */
+public class ExerciseThird {
+    public static void main(String[] args) {
+        List<Student> students = new ArrayList<>();
+        students.add(new Student("张三", 20, Gender.MALE));
+        students.add(new Student("李希", 39, Gender.MALE));
+        students.add(new Student("小七", 18, Gender.FEMALE));
+        ListIterator<Student> iterator = students.listIterator();
+        int age = 0;
+        int index = -1;
+        while (iterator.hasNext()) {
+            int idx = iterator.nextIndex();
+            Student student = iterator.next();
+            System.out.println(student);
+            if (student.getAge() > age) {
+                age = student.getAge();
+                index = idx;
+            }
+        }
+        students.get(index).setName("葫芦娃");
+        System.out.println(students.get(index));
+    }
+
+
+}
+enum Gender {
+    MALE ("男"), FEMALE ("女");
+
+    private final String name;
+
+    Gender(String s) {
+        name = s;
+    }
+
+    @Override
+    public String toString() {
+        return name;
+    }
+
+    public String getName() {
+        return name;
+    }
+}
+
+class Student {
+    private String name;
+    private int age;
+    private Gender gender;
+
+    public Student(String name, int age, Gender gender) {
+        this.name = name;
+        this.age = age;
+        this.gender = gender;
+    }
+
+    @Override
+    public String toString() {
+        return String.format("姓名 %s 年龄 %d 性别 %s", name, age, gender.getName());
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+}