Uniqueness and ordering in set

1. Remove duplicate values

stay List Remove duplicate numeric values from the set , The requirements are as simple as possible （ With the help of other sets ！！）

package com.B.Container_13.Set.MAp.Practice;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;

// stay List Remove duplicate numeric values from the set , The requirements are as simple as possible （ With the help of other sets ！！）
public class A5 {
    public static void main(String[] args) {
//         establish list A collection of objects 
        ArrayList<Integer> list = new ArrayList<Integer>();
//         Additive elements 
        list.add(12);
        list.add(15);
        list.add(24);
        list.add(12);
        list.add(24);
//         establish set aggregate 
        HashSet<Integer> set = new HashSet<Integer>();
//         Create a new list aggregate 
        List newList = new  ArrayList();
// take list The elements of the collection are added to set aggregate , Achieve the purpose of removing duplicate numerical values 
        for (Integer s :list) {
            if(set.add(s)){
                newList.add(s);
            }
        }
        System.out.println( " The collection after de duplication ： " + newList);
    }
}


 Output ：
 The collection after de duplication ： [12, 15, 24]

 Process ended , Exit code  0

2. Remove duplicate values

There are several books and information （ Include name title、 author author、 pricing price） Need to store to set Collection , Ensure that there are no duplicate elements in the collection , And traverse to see . It can be considered that all books with the same information are duplicate data .

    package com.B.Container_13.Set.MAp.Practice;
// Books and information （ Include name title、 author author、 pricing price）
public class A7_books {
    private String title;
    private String author;
    private double price;

    public A7_books() {
    }

    public A7_books(String title, String author, double price) {
        this.title = title;
        this.author = author;
        this.price = price;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

//     Rewriting methods 

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        A7_books a7_01 = (A7_books) o;

        if (Double.compare(a7_01.price, price) != 0) return false;
        if (title != null ? !title.equals(a7_01.title) : a7_01.title != null) return false;
        return author != null ? author.equals(a7_01.author) : a7_01.author == null;
    }

    @Override
    public int hashCode() {
        int result;
        long temp;
        result = title != null ? title.hashCode() : 0;
        result = 31 * result + (author != null ? author.hashCode() : 0);
        temp = Double.doubleToLongBits(price);
        result = 31 * result + (int) (temp ^ (temp >>> 32));
        return result;
    }
}

 Test class ：
package com.B.Container_13.Set.MAp.Practice;

import java.util.HashSet;

// There are several books and information （ Include name title、 author author、 pricing price）
//  Need to store to set Collection , Ensure that there are no duplicate elements in the collection , And traverse to see . It can be considered that all books with the same information are duplicate data .
public class A7 {
    public static void main(String[] args) {
// Create objects 
        HashSet<A7_books> hs = new HashSet<A7_books>();
// Additive elements 
        A7_books book1 = new A7_books(" Journey to the west "," Wu chengen ",69.9);
        A7_books book2 = new A7_books(" The romance of The Three Kingdoms "," Luo Guanzhong ",59.9);
        A7_books book3 = new A7_books(" Journey to the west "," Wu chengen ",69.9);
        A7_books book4 = new A7_books(" A dream of red mansions "," Cao xueqin ",58.9);
        A7_books book5 = new A7_books(" Water margin "," Shi Naian ",46.9);

        hs.add(book1);
        hs.add(book2);
        hs.add(book3);
        hs.add(book4);
        hs.add(book5);

// Output 
        for (A7_books h : hs) {
            System.out.println("《"+h.getTitle()+"》 The author is "+h.getAuthor()+", The price for "+h.getPrice()+" element ");
        }
Tom

    }
}

 Output results ：
《 Water margin 》 The author is Shi Naian , The price for 46.9 element 
《 A dream of red mansions 》 The author is Cao Xueqin , The price for 58.9 element 
《 Journey to the west 》 The author is Wu Chengen , The price for 69.9 element 
《 The romance of The Three Kingdoms 》 The author is Luo Guanzhong , The price for 59.9 element 

 Process ended , Exit code  0

3. Sort （ There are priorities ）

In an exam , The student's grade information is as follows （ Public attribute ）： full name (String) Age （int） achievement (int): Tom 20 90; Jerry 22 95; John 20 100; Lily 22 100 ;Lucy 22 90; Kevin 22 90 Please use... Separately Comparable and Comparator The two interfaces sort the grades of the above students in descending order , If the results are the same , Based on the ranking of grades, they are ranked according to their age , Grades and age are the same , Then sort according to the dictionary order of names .

What happened ：

The output results are not in descending order

Reasons for appearance ：

Wrong sorting logic

  Improvement measures ：

In exchange for s1 and s2 Location

  Complete code ：

Comparable Interface sorting ：
package com.B.Container_13.Set.MAp.Practice;
//Comparable Interface sorting 
// Students 
// In an exam , The student's grade information is as follows （ Public attribute ）：  full name (String)  Age （int）  achievement (int)
//Tom 20 90; Jerry 22 95; John 20 100; Lily 22 100 ;Lucy 22 90; Kevin 22 90
public class A8_Student01 implements Comparable<A8_Student01> {
    private String name;
    private int age;
    private int score;

    public A8_Student01() {
    }

    public A8_Student01(String name, int age, int score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    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;
    }

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }

    @Override
    public int compareTo(A8_Student01 s) {
        //     Grades are sorted in descending order , From big to small 
        int num = s.score - this.score;
        // At the same age , Sort by age 
        int num1 = num == 0 ? this.age - s.age : num;
//         Grades and age are the same , Then sort according to the dictionary order of names .
        int num2 = num1 == 0 ? this.name.compareTo(s.name) : num1;
        return num2;
    }

}

 Test class ：
    package com.B.Container_13.Set.MAp.Practice;
//Comparable Interface sorting 

// Please use... Separately Comparable and Comparator The two interfaces sort the grades of the above students in descending order ,
// If the results are the same , Based on the ranking of grades, they are ranked according to their age ,
//  Grades and age are the same , Then sort according to the dictionary order of names .

import java.util.TreeSet;

public class A8_01 {
    public static void main(String[] args) {
        // Create a collection object 
        TreeSet<A8_Student01> stu = new TreeSet<A8_Student01>();
// Create student objects 
        A8_Student01 s1 = new A8_Student01("Tom", 20,90);
        A8_Student01 s2 = new A8_Student01("Jerry", 22,95);
        A8_Student01 s3 = new A8_Student01("John", 20,100);
        A8_Student01 s4 = new A8_Student01("Lily", 22,100);
        A8_Student01 s5 = new A8_Student01("Lucy", 22,90);
        A8_Student01 s6 = new A8_Student01("Kevin", 22,90);
        // Add students to the collection 
        stu.add(s1);
        stu.add(s2);
        stu.add(s3);
        stu.add(s4);
        stu.add(s5);
        stu.add(s6);

        // Ergodic set 
        for (A8_Student01 s : stu) {
            System.out.println(s.getName() +","+s.getAge()+","+s.getScore());
        }

    }
}


 Running results ：
 John,20,100
Lily,22,100
Jerry,22,95
Tom,20,90
Kevin,22,90
Lucy,22,90

 Process ended , Exit code  0
    
Comparator Interface sorting ：
   package com.B.Container_13.Set.MAp.Practice;

Comparator Interface sorting 
// In an exam , The student's grade information is as follows （ Public attribute ）：  full name (String)  Age （int）  achievement (int):
public class A8_Student02 {
    String name;
    int age;
    int score;

    public A8_Student02() {
    }

    public A8_Student02(String name, int age, int score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    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;
    }

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }

    @Override
    public String toString() {
        return "A8_Student02{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", score=" + score +
                '}';
    }
}

 Test class ：
package com.B.Container_13.Set.MAp.Practice;

import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;

//Comparator Interface sorting 
public class A8_02 {
    public static void main(String[] args) {
// Create a TreeSet A collection of objects 
Set<A8_Student02> treeSet =new TreeSet<A8_Student02>(new Comparator<A8_Student02>() {
    @Override
    public int compare(A8_Student02 s1, A8_Student02 s2) {
        //     Grades are sorted in descending order , From big to small 
        int num = s2.getScore() - s1.getScore();
        // At the same age , Sort by age 
        int num1 = num == 0 ? s1.getAge() - s2.getAge() : num;
//         Grades and age are the same , Then sort according to the dictionary order of names .
        int num2 = num1 == 0 ? s1.getName().compareTo(s2.getName()) : num1;
        return num2;
    }
});

// Create student objects 
        treeSet.add(new A8_Student02("Tom", 20,90));
        treeSet.add(new A8_Student02("Jerry", 22,95));
        treeSet.add(new A8_Student02("John", 20,100));
        treeSet.add(new A8_Student02("Lily", 22,100));
        treeSet.add(new A8_Student02("Lucy", 22,90));
        treeSet.add(new A8_Student02("Kevin", 22,90));

// Traversal array 
        for (A8_Student02 s02 : treeSet) {
            System.out.println(s02);
        }

    }
}

 result ：
 A8_Student02{name='John', age=20, score=100}
A8_Student02{name='Lily', age=22, score=100}
A8_Student02{name='Jerry', age=22, score=95}
A8_Student02{name='Tom', age=20, score=90}
A8_Student02{name='Kevin', age=22, score=90}
A8_Student02{name='Lucy', age=22, score=90}

 Process ended , Exit code  0