Java语法基础50题训练(下)
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题目1:
HashMap集合存储学生对象并遍历。
需求:
创建一个HashMap集合，键是学生对象(Student)，值是居住地(String)。存储多个键值对象，并遍历。
要求:
保证键的唯一性：如果学生对象的成员变量值相同，我们就认为是同一个对象。
代码如下:
package HashMapPrintPack02;
public class Student {
private String name;
private int age;
public Student() {
}
public Student(String name, int age) {
this.name = name;
this.age = age;
}
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;
}
@Override
public 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;
}
@Override
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + age;
return result;
}
}
package HashMapPrintPack02;
import java.util.HashMap;
import java.util.Set;
public class HashMapDemo {
public static void main(String[] args)
{
HashMap<Student,String> hs = new HashMap<Student,String>();
Student s1 = new Student("Tom",30);
Student s2 = new Student("Jack",28);
Student s3 = new Student("Lily",17);
Student s4 = new Student("Tom",30);
hs.put(s1,"西安");
hs.put(s2,"北京");
hs.put(s3,"上海");
hs.put(s4,"深圳");
Set<Student> keySet = hs.keySet();
for (Student key:keySet)
{
String value = hs.get(key);
System.out.println(key.getName()+","+key.getAge()+","+value);
}
}
}
题目2:
ArrayList集合存储HashMap元素并遍历。
需求:
创建一个ArrayList集合，存储三个元素，每一个元素都是HashMap，每一个HashMap的键和值都是String，并遍历。
代码如下:
package ArrayListAndHashMapPack01;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Set;
public class ArrayListIncludeHashMapDemo {
public static void main(String[] args)
{
ArrayList<HashMap<String,String>> array = new ArrayList<HashMap<String, String>>();
HashMap<String,String> hm1 = new HashMap<String,String>();
hm1.put("Tom","Jack");
hm1.put("Bom","Lily");
array.add(hm1);
HashMap<String,String> hm2 = new HashMap<String,String>();
hm1.put("小明","小红");
hm1.put("小兰","小绿");
array.add(hm2);
HashMap<String,String> hm3 = new HashMap<String,String>();
hm1.put("Mike","Zliy");
hm1.put("Bo","Db");
array.add(hm3);
for(HashMap<String,String> hm:array)
{
Set<String> keySet = hm.keySet();
for (String key:keySet)
{
String value = hm.get(key);
System.out.println(key+","+value);
}
}
}
}
题目3:
HashMap集合存储ArrayList元素并遍历。
需求:
创建一个HashMap集合，存储三个键值对元素，每一个键值对元素的键是String，值是ArrayList，每一个ArrayList的元素是String，并遍历。
代码如下:
package HashMapIncludeArrayListPack;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Set;
public class HashMapIncludeArrayListDemo {
public static void main(String[] args)
{
HashMap<String, ArrayList<String>> hm = new HashMap<String,ArrayList<String>>();
ArrayList<String> sgyy = new ArrayList<String>();
sgyy.add("赵云");
sgyy.add("刘备");
hm.put("三国演义",sgyy);
ArrayList<String> xyj = new ArrayList<String>();
xyj.add("唐僧");
xyj.add("猴哥");
hm.put("西游记",xyj);
ArrayList<String> hlm = new ArrayList<String>();
hlm.add("贾宝玉");
hlm.add("林黛玉");
hm.put("红楼梦",hlm);
Set<String> keySet = hm.keySet();
for (String key:keySet)
{
System.out.println(key);
ArrayList<String> value = hm.get(key);
for (String s:value)
{
System.out.println("\\t"+s);
}
}
}
}
题目4:
统计字符串中每个字符串出现的次数。
需求:
键盘录入一个字符串，要求统计字符串中每个字符串出现的次数。
举例：
键盘录入"aababcabcdabcde",在控制台输出:“a(5)b(4)c(3)d(2)e(1)”
代码如下:
package CountStringNumPack;
import java.util.HashMap;
import java.util.Scanner;
import java.util.Set;
public class HashMapDemp {
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
System.out.println("请输入一个字符串");
String line = sc.nextLine();
HashMap<Character,Integer> hm = new HashMap<Character,Integer>();
for (int i = 0;i<line.length();i++)
{
char key = line.charAt(i);
Integer value = hm.get(key);
if (value==null)
{
hm.put(key,1);
}
else {
value++;
hm.put(key, value);
}
}
StringBuilder sb = new StringBuilder();
Set<Character> keySet = hm.keySet();
for (Character key:keySet)
{
Integer value = hm.get(key);
sb.append(key).append("(").append(value).append(")");
}
String ans = sb.toString();
System.out.println(ans);
}
}
package CountStringNumPack;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeMap;
public class HashMapDemp {
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
System.out.println("请输入一个字符串");
String line = sc.nextLine();
TreeMap<Character,Integer> hm = new TreeMap<Character,Integer>();
for (int i = 0;i<line.length();i++)
{
char key = line.charAt(i);
Integer value = hm.get(key);
if (value==null)
{
hm.put(key,1);
}
else {
value++;
hm.put(key, value);
}
}
StringBuilder sb = new StringBuilder();
Set<Character> keySet = hm.keySet();
for (Character key:keySet)
{
Integer value = hm.get(key);
sb.append(key).append("(").append(value).append(")");
}
String ans = sb.toString();
System.out.println(ans);
}
}
题目5:
ArrayList存储学生对象并排序。
需求:
ArrayList存储学生对象，使用Collections对ArrayList进行排序。
要求:
按照年龄从小到大排序，年龄相同时，按照姓名的字母顺序排序。
代码如下:
package CollectionsDemo02;
public class Student {
private String name;
private int age;
public Student() {
}
public Student(String name, int age) {
this.name = name;
this.age = age;
}
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;
}
}
package CollectionsDemo02;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
public class CollectionsDemo02 {
public static void main(String[] args)
{
ArrayList<Student> array = new ArrayList<Student>();
Student s1 = new Student("Tom",18);
Student s2 = new Student("Jack",20);
Student s3 = new Student("Bom",29);
Student s4 = new Student("Lily",23);
array.add(s1);
array.add(s2);
array.add(s3);
array.add(s4);
Collections.sort(array, new Comparator<Student>() {
@Override
public int compare(Student s1, Student s2) {
int num = s1.getAge()-s2.getAge();
int num2 = num==0?s1.getName().compareTo(s2.getName()):num;
return num2;
}
});
for (Student s:array)
{
System.out.println(s.getName()+","+s.getAge(2019年最新50道java基础部分面试题