2021-05-10

课堂代码

import java.lang.reflect.Array;
import java.util.*;

public class Demo03 {
    public static void main(String[] args) {
        HashMap<String,String> map = new HashMap<>();
        map.put("1","A");
        map.put("2","B");
        map.put("3","C");
        // 1
        Set<String>keys = map.keySet();
        System.out.println(keys);
        // 2 把set转换成其他集合
        ArrayList<String>alistkeys = new ArrayList<>(keys);
        System.out.println(alistkeys);
        // 3 取出map的值 value()
        Collection<String> v = map.values();
        System.out.println(v);
        // 4 把值转换成其他的集合，new LinkedList(v)
        LinkedList<String> llistv = new LinkedList<>(v);
        System.out.println(llistv);
    }
}

import java.rmi.activation.ActivationSystem;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class Demo04 {
    public static void main(String[] args) {
        HashMap<Integer,String> map = new HashMap<>();
        for ( int i = 0 ;  i < 2000; i++ ){
            map.put(i,"haha" + i);
        }
        Iterator<Map.Entry<Integer,String>> iterator = map.entrySet().iterator();
        while(iterator.hasNext()){
            Map.Entry<Integer,String> next = iterator.next();
            System.out.println(next);
        }

    }
}

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.concurrent.Callable;

public class Demo05 {
    public static void main(String[] args) {
        ArrayList nums = new ArrayList<>();
        nums.add(2);
        nums.add(0);
        nums.add(-5);
        nums.add(0);
        nums.add(3);

        // 1 排序sort
        Collections.sort(nums);
        System.out.println(nums);
        // 2 反转reverse
        Collections.sort(nums);
        System.out.println(nums);
        System.out.println(nums);
        // 3 混洗
        Collections.shuffle(nums);
        System.out.println(nums);
        // 4 求最大小值
        System.out.println(Collections.max(nums));
        System.out.println(Collections.min(nums));
        // 5 替换'
        Collections.replaceAll(nums,0,100);
        System.out.println(nums);
        // 6 求频率
        System.out.println(Collections.frequency(nums,100));
        // 7 二分搜索 ， 使用的条件是集合是有序的
        Collections.sort(nums);
        System.out.println(nums);
        int i = Collections.binarySearch(nums,3);
        System.out.println("位置" + i);
    }
}

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public class Demo {
    public static void main(String[] args) {
        ArrayList<User> list = new ArrayList<>();
        User zhangsan = new User(15,"zhangsan",98);
        User lisi = new User(13,"lisi",88);
        User wangwu = new User(16,"wangwu",68);
        list.add(zhangsan);
        list.add(lisi);
        list.add(wangwu);
        System.out.println(list);
        Collections.sort(list, new Comparator<User>() {
            @Override
            public int compare(User o1, User o2) {
                return o1.getUid() - o2.getUid();
            }
        });
        System.out.println(lisi);
    }
}

import javax.jws.soap.SOAPBinding;

public class User {
    private Integer uid;
    private String name;
    private Integer grade;
    public User(){
    }
    public User(Integer uid,String name ,Integer grade){
        this.uid = uid;
        this.name = name;
        this.grade = grade;
    }
    public Integer getUid(){
        return uid;
    }
    public void setUid(Integer uid){
    }
    public String  getname(){
        return name;
    }
    public void setName(String name){
    }
    public Integer getGrade(){
        return grade;
    }
    public void setGrade(Integer grade){
        this.grade = grade;
    }
    @Override
    public String toString(){
        return "User{"+
                "uid="+uid +
                ",name='" + name + '\''+
                ",grade ="+ grade+
                '}';
    }

}