Java教程
Java自学-集合(5)
本文主要是介绍Java自学-集合(5)，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！
Java自学-集合(5)
1、Set集合概述和特点
package lesson01;
import java.util.HashSet;
import java.util.Set;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 15:26
* FileName: SetDemo
* Description:
*/
public class SetDemo {
public static void main(String[] args) {
Set<String> set=new HashSet<String>();
set.add("hello");
set.add("world");
set.add("java");
set.add("world");
for(String s:set){
System.out.println(s);
}
}
}
2、哈希值
Student.java
package lesson01;
import java.util.Objects;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 15:31
* FileName: Student
* Description:
*/
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;
return age == student.age && Objects.equals(name, student.name);
}
@Override
public int hashCode() {
return 0;
}
}
HashDemo.java
package lesson01;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 15:30
* FileName: HashDemo
* Description:
*/
public class HashDemo {
public static void main(String[] args) {
Student s1=new Student("蔡伟",1);
///同一个对象多次调用hashCode()方法返回的哈希值是相同的。
System.out.println(s1.hashCode());
System.out.println(s1.hashCode());
System.out.println("--------");
//默认情况下，不同对象的哈希值是不相同的。
//通过方法重写，可以实现不同对象的哈希值是相同的。
Student s2=new Student("蔡伟",1);
System.out.println(s2.hashCode());
System.out.println(s2.hashCode());
System.out.println("hello".hashCode());
System.out.println("world".hashCode());
System.out.println("java".hashCode());
System.out.println("world".hashCode());
System.out.println("--------");
System.out.println("重地".hashCode());
System.out.println("通话".hashCode());
}
}
3、HashSet集合概述和特点
package lesson01;
import java.util.HashSet;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 15:43
* FileName: HashSetDemo01
* Description:
*/
public class HashSetDemo01 {
public static void main(String[] args) {
HashSet<String> hs = new HashSet<>();
hs.add("hello");
hs.add("world");
hs.add("java");
hs.add("world");
for(String s:hs){
System.out.println(s);
}
}
}
4、HashSet集合保证元素唯一性源码分析
5、常见数据结构之哈希表
6、HashSet集合存储学生对象并遍历
Student.java
package lesson02;
import java.util.Objects;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 15:31
* FileName: Student
* Description:
*/
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;
return age == student.age && Objects.equals(name, student.name);
}
@Override
public int hashCode() {
return Objects.hash(name, age);
}
}
HashSetDemo02.java
package lesson02;
import java.util.HashSet;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 16:06
* FileName: HashSetDemo02
* Description:
*/
public class HashSetDemo02 {
public static void main(String[] args) {
HashSet<Student> hs=new HashSet<Student>();
Student s1 = new Student("蔡伟1号", 1);
Student s2 = new Student("蔡伟2号", 1);
Student s3 = new Student("蔡伟3号", 1);
Student s4 = new Student("蔡伟3号", 1);
hs.add(s1);
hs.add(s2);
hs.add(s3);
hs.add(s4);
for(Student s:hs){
System.out.println(s.getName()+","+s.getAge());
}
}
}
7、LinkedHashSet集合概述和特点
package lesson02;
import java.util.LinkedHashSet;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 16:14
* FileName: LinkedHashSetDemo
* Description:
*/
public class LinkedHashSetDemo {
public static void main(String[] args) {
LinkedHashSet<String> strings = new LinkedHashSet<>();
strings.add("hello");
strings.add("world");
strings.add("java");
strings.add("world");
for(String s:strings){
System.out.println(s);
}
}
}
8、TreeSet集合概述和特点
集合只能存储引用类型。
package lesson02;
import java.util.TreeSet;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 16:19
* FileName: TreeSetDemo01
* Description:
*/
public class TreeSetDemo01 {
public static void main(String[] args) {
TreeSet<Integer> ts = new TreeSet<>();
ts.add(10);
ts.add(40);
ts.add(30);
ts.add(50);
ts.add(20);
ts.add(30);
for(Integer i :ts){
System.out.println(i);
}
}
}
9、自然排序Comparable的使用
Student.java
package lesson03;
import java.util.Objects;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 15:31
* FileName: Student
* Description:
*/
public class Student implements Comparable<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 int compareTo(Student s) {
// return 0;
// return 1;//升序
// return -1;//降序
// 按照年龄从小到大排序。
int num=this.age-s.age;
// int num=s.age-this.age;
// 年龄相同时，按照姓名的字母顺序排序。
int num2=num==0?this.name.compareTo(s.name):num;
return num2;
}
}
TreeSetDemo02.java
package lesson03;
import java.util.TreeSet;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 16:23
* FileName: TreeSetDemo02
* Description:
*/
public class TreeSetDemo02 {
public static void main(String[] args) {
TreeSet<Student> ts = new TreeSet<Student>();
Student s1 = new Student("xishi",1);
Student s2 = new Student("wangzhaojun",3);
Student s3 = new Student("diaochan",2);
Student s4 = new Student("yangyvhuan",4);
Student s5 = new Student("caiwei",4);
Student s6 = new Student("caiwei",4);
ts.add(s1);
ts.add(s2);
ts.add(s3);
ts.add(s4);
ts.add(s5);
for(Student s:ts){
System.out.println(s.getName()+","+s.getAge());
}
}
}
10、比较器排序Comparator的使用
Student.java
package lesson04;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 15:31
* FileName: Student
* Description:
*/
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;
}
}
TreeSetDemo.java
package lesson04;
import java.util.Comparator;
import java.util.TreeSet;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 16:47
* FileName: TreeSetDemo
* Description:
*/
public class TreeSetDemo {
public static void main(String[] args) {
TreeSet<Student> ts = new TreeSet<>(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;
}
});
Student s1 = new Student("xishi",1);
Student s2 = new Student("wangzhaojun",3);
Student s3 = new Student("diaochan",2);
Student s4 = new Student("yangyvhuan",4);
Student s5 = new Student("caiwei",4);
Student s6 = new Student("caiwei",4);
ts.add(s1);
ts.add(s2);
ts.add(s3);
ts.add(s4);
ts.add(s5);
for(Student s:ts){
System.out.println(s.getName()+","+s.getAge());
}
}
}
11、成绩排序
IDEA快捷键：Ctrl+alt+l
Student.java
package lesson05;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 16:59
* FileName: Student
* Description:
*/
public class Student {
private String name;
private int chinese;
private int math;
public Student() {
}
public Student(String name, int chinese, int math) {
this.name = name;
this.chinese = chinese;
this.math = math;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getChinese() {
return chinese;
}
public void setChinese(int chinese) {
this.chinese = chinese;
}
public int getMath() {
return math;
}
public void setMath(int math) {
this.math = math;
}
public int getSum() {
return this.getChinese() + this.getMath();
}
}
TreeSetDemo.java
package lesson05;
import java.util.Comparator;
import java.util.TreeSet;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 16:59
* FileName: TreeSetDemo
* Description:
*/
public class TreeSetDemo {
public static void main(String[] args) {
TreeSet<Student> ts = new TreeSet<>(new Comparator<Student>() {
@Override
public int compare(Student s1, Student s2) {
//主要条件
int num=s2.getSum()-s1.getSum();
//次要条件
int num2=num==0?s1.getChinese()-s2.getChinese():num;
int num3=num2==0?s1.getName().compareTo(s2.getName()):num2;
return num3;
}
});
Student s1= new Student("小火猴",95,20);
Student s2 = new Student("布布种子",60,75);
Student s3 = new Student("巴鲁斯",62,75);
Student s4 = new Student("哈默",60,60);
Student s5 = new Student("满分君",100,100);
Student s6 = new Student("盖亚",100,100);
ts.add(s1);
ts.add(s2);
ts.add(s3);
ts.add(s4);
ts.add(s5);
ts.add(s6);
for(Student s:ts){
System.out.println(s.getName()+","+s.getChinese()+","+s.getMath()+","+s.getSum());
}
}
}
12、不重复的随机数
package lesson05;
import java.util.HashSet;
import java.util.Random;
import java.util.Set;
import java.util.TreeSet;
/**
* Author: Gu Jiakai
* Date: 2021/8/16 17:17
* FileName: SetDemo
* Description:
*/
public class SetDemo {
public static void main(String[] args) {
// Set<Integer> set=new HashSet<Integer>();
Set<Integer> set=new TreeSet<Integer>();
Random random = new Random();
while(set.size()<10){
int i = random.nextInt(20) + 1;
set.add(i);
}
for(Integer i:set){
System.out.println(i);
}
}
}
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