Map集合相关应用

1.键盘录入一个字符串，求该字符串中每一个字符出现的次数。
要求：按照字母顺序打印
如: 录入的字符串为"apple"，打印 a(1) e(1) l(1) p(2)

public class Demo4 {public static void main(String[] args) {//键盘录入Scanner sc = new Scanner(System.in);System.out.println("请输入字符串");String str = sc.nextLine();//创建treeMap存储字符【键】，个数【值】TreeMap<Character, Integer> map = new TreeMap<>();//遍历输入的字符串//方法一：str.length()， str.charAt(i)得到每一个字符for (int i = 0; i < str.length(); i++) {//得到每一个字符char ch = str.charAt(i);//判断键在集合中是否存在if(map.containsKey(ch)){//如果存在，则获取对应的值Integer value = map.get(ch);//将值+1并存入集合中map.put(ch,value+1);}//否则不存在，则值为1，直接存入else {map.put(ch,1);}}//方法二：s/*char[] charArr = str.toCharArray();for (int i = 0; i < charArr.length; i++) {if(map.containsKey(charArr[i])){//如果存在，则获取对应的值Integer value = map.get(charArr[i]);//将值+1并存入集合中map.put(charArr[i],value+1);}//否则不存在，则值为1，直接存入else {map.put(charArr[i],1);}}*///打印集合//录入的字符串为"apple"，打印 a(1) e(1) l(1) p(2)Set<Map.Entry<Character, Integer>> entries = map.entrySet();for (Map.Entry<Character, Integer> entry : entries) {System.out.print(entry.getKey()+"("+entry.getValue()+")"+" ");}System.out.println();}
}打印结果：
-----------------------------------------------------------------
请输入字符串
asdagfasfas
a(4) d(1) f(2) g(1) s(3)

使用HashMap集合存储Student对象作为键，学生的家庭住址作为值
要求：要求学生的姓名和年龄不能重复
使用TreeMap集合存储Student对象作为键，学生的家庭住址作为值
要求：先按照年龄进行排序，再按照姓名进行排序

测试类：
public class Demo3 {public static void main(String[] args) {//1. 使用HashMap集合存储Student对象作为键，学生的家庭住址作为值//		要求：要求学生的姓名和年龄不能重复HashMap<Student, String> hashMap = new HashMap<>();hashMap.put(new Student("张三",20),"武汉");hashMap.put(new Student("李四",21),"孝感");hashMap.put(new Student("王五",20),"武汉");hashMap.put(new Student("张三",22),"安陆");hashMap.put(new Student("张三",20),"汉川");//键值对遍历Set<Map.Entry<Student, String>> entries = hashMap.entrySet();for (Map.Entry<Student, String> entry : entries) {System.out.println(entry.getKey()+"..."+entry.getValue());}//2. 使用TreeMap集合存储Student对象作为键，学生的家庭住址作为值//		要求：先按照年龄进行排序，再按照姓名进行排序System.out.println("----------------------");TreeMap<Student, String> treeMap = new TreeMap<>();treeMap.put(new Student("zhangsan",20),"武汉");treeMap.put(new Student("lisi",21),"孝感");treeMap.put(new Student("wangwu",20),"武汉");treeMap.put(new Student("zhangsan",22),"安陆");treeMap.put(new Student("zhangsan",20),"汉川");//键找值遍历Set<Student> keys = treeMap.keySet();for (Student key : keys) {String value = treeMap.get(key);System.out.println(key+"..."+value);}}
}打印结果：
---------------------------------------------------------------
Student{name='王五', age=20}...武汉
Student{name='张三', age=22}...安陆
Student{name='张三', age=20}...汉川
Student{name='李四', age=21}...孝感
----------------------
Student{name='wangwu', age=20}...武汉
Student{name='zhangsan', age=20}...汉川
Student{name='lisi', age=21}...孝感
Student{name='zhangsan', age=22}...安陆

学生类

public class Student implements Comparable<Student> {private String name;private int  age;public Student(String name, int age) {this.name = name;this.age = age;}public Student() {}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", age=" + age +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Student student = (Student) o;if (age != student.age) return false;return name != null ? name.equals(student.name) : student.name == null;}@Overridepublic int hashCode() {int result = name != null ? name.hashCode() : 0;result = 31 * result + age;return result;}@Overridepublic int compareTo(Student o) {int result =this.age-o.age;result = result == 0 ? this.getName().compareTo(o.getName()) : result;return result;}
}