java集合工具类

//集合类工具
//集合类工具Collection:排序,复制,反转等操作
//数组工具类Arrays:排序,复制,反转等操作
package col;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;

public class Demo6 {

    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("w");
        list.add("a");
        list.add("b");
        list.add("x");
        list.add("a");
        list.add("i");
        Collections.sort(list);
        System.out.println(list);
        System.out.println(Collections.max(list));
        System.out.println(Collections.min(list));
        // 二分查找法,(使用前必须保证有序)
        System.out.println(Collections.binarySearch(list, "i"));
        // 混洗，洗牌：打乱已有顺序
        Collections.shuffle(list);
        System.out.println(list);
        Collections.reverse(list);
        System.out.println(list);
        Collections.swap(list, 2, 3);
        System.out.println(list);
        Collections.replaceAll(list, "a", "A");
        System.out.println(list);
        Collections.fill(list, "H");
        System.out.println(list);
    }

}

 

package col;

import java.util.Arrays;

public class Demo7 {

    public static void main(String[] args) {
        int[] arr = new int[] { 5, 4, 3, 8, 2, 9 };
        Arrays.sort(arr);
        for (int x : arr) {
            System.out.print(x + " ");
        }
        System.out.println();
        /*Arrays.fill(arr, 5);
        for (int x : arr) {
            System.out.print(x + " ");
        }*/
        int pos=Arrays.binarySearch(arr, 3);
        System.out.println(pos);
    }

}

package col;

public class Student implements Comparable {
    private int id;
    private String name;
    private int age;
    private String city;
    public Student() {
    }
    public Student(int id, String name, int age, String city) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
        this.city = city;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    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 String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", age=" + age + ", city=" + city + "]";
    }
     //重写比较器接口中的方法

    /*
        {1,3,5,7  }升序
        {7,5,3,1  }降序
        //输入源   3     1  7  5
           {3}

        返回值：
            1正数：当前对象大，    降序
     -1负数：传入的对象大 ，升序
            0：一样大
    */
    
    public int compareTo(Object o) {
        Student inputstudent=(Student)o;
        //根据学号排序,降序
        int result =this.id>inputstudent.id?-1:(   this.id   ==    inputstudent.id ?0:1 );
          //int result =this.id<inputstudent.id?1:(   this.id   ==    inputstudent.id ?0:-1 );
        if(result==0) {
            result=this.name.compareTo(inputstudent.name);
        }
        return result;
        //return 1;//当前对象，比传入对象大
    }
}

package col;

public class Teacher {
    private int id;
    private String name;
    private int age;
    private String city;
    public Teacher(int id, String name, int age, String city) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.city = city;
    }
    public Teacher() {
        super();
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    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 String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    @Override
    public String toString() {
        return "Teacher [id=" + id + ", name=" + name + ", age=" + age + ", city=" + city + "]";
    }
    
}

package col;

import java.util.Comparator;

/*思路：将比较的对象（Student）实现Comparable接口，
 * 重写连的compareTo()方法。在compareTo()中编写比较的逻辑。重点是返回值，-1 ，0,1  ；  
Comparator：外部比较器 （无侵入性，不影响原有代码）
先定义一个外部比较器*/
public class MyComparatorWithId implements Comparator {

    @Override
    public int compare(Object o1, Object o2) {
        Teacher t1=(Teacher)o1;
        Teacher t2=(Teacher)o2;
        return t2.getId()-t1.getId();
    }
    
     
}

package col;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Demo8 {
     //内部比较器
    public static void main(String[] args) {
        List<Student> students = new ArrayList<>();
        Student s1 = new Student(10, "张三", 23, "阜阳");
        Student s2 = new Student(15, "李四", 21, "亳州");
        Student s3 = new Student(13, "王二", 26, "宿州");
        Student s4 = new Student(17, "麻子", 65, "合肥");
        students.add(s1);
        students.add(s2);
        students.add(s3);
        students.add(s4);
        Collections.sort(students);
        System.out.println(students);
        System.out.println("-------");
        
        Teacher t1=new Teacher(12, "贤明", 56, "山东");
        Teacher t2=new Teacher(42, "大明", 16, "贵州");
        Teacher t3=new Teacher(13, "小明", 76, "四川");
        List<Teacher> teachers=new ArrayList<Teacher>();
        teachers.add(t1);
        teachers.add(t2);
        teachers.add(t3);
        Collections.sort(teachers, new MyComparatorWithId());
        System.out.println(teachers);
    }
    
}