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+
'}';
}
}