目录
第三章.Random类
1.概述
2.Random类的使用
(1)无参
package day32;
import java.util.Random;
public class Demo01 {
public static void main(String[] args) {
Random r = new Random();
int num = r.nextInt();
System.out.println("随机数为 : " + num);
}
}
(2)有参
package day32;
import java.util.Random;
public class Demo02 {
public static void main(String[] args) {
Random r = new Random();
for (int i = 0; i < 100; i++) {
int num = r.nextInt(9);
System.out.println("随机数为 : " + num);
}
}
}
3.练习
（1）
package day32;
import java.util.Random;
public class Demo03 {
public static void main(String[] args) {
Random r = new Random();
int n = 5;
for (int i = 0; i < 10; i++) {
int num = r.nextInt(n) + 1;
System.out.println("随机数为 : " + num);
}
}
}
（2）
package day32;
import java.util.Random;
import java.util.Scanner;
public class Demo04 {
public static void main(String[] args) {
Random r = new Random();
int n = r.nextInt(100) + 1;
Scanner sc = new Scanner(System.in);
while (true) {
System.out.println("请输入你猜测的数字 ： ");
int i = sc.nextInt();
if (i > n) {
System.out.println("抱歉，您猜测的数字太大了.请重试");
} else if (i < n) {
System.out.println("抱歉，您猜测的数字太小了.请重试");
} else {
System.out.println("恭喜你，猜对了");
break;
}
}
System.out.println("游戏结束了！");
}
}
(3)规定次数
5.规定次数的情况需要用for循环
package day32;
import java.util.Random;
import java.util.Scanner;
public class Demo05 {
public static void main(String[] args) {
Random r = new Random();
int n = r.nextInt(100) + 1;
Scanner sc = new Scanner(System.in);
for (int i = 1; i <= 10; i++) {
System.out.println("请输入你猜测的数字 ： ");
int g = sc.nextInt();
if (g > n) {
System.out.println("抱歉，您猜测的数字太大了.请重试");
} else if (g < n) {
System.out.println("抱歉，您猜测的数字太小了.请重试");
} else {
System.out.println("恭喜你，猜对了");
break;
}
System.out.println("您还有" + (10 - i) + "次机会");
}
System.out.println("游戏结束了！");
}
}
4.对象数组
package day32;
import java.util.Random;
import java.util.Scanner;
public class Demo05 {
public static void main(String[] args) {
Random r = new Random();
int n = r.nextInt(100) + 1;
Scanner sc = new Scanner(System.in);
for (int i = 1; i <= 10; i++) {
System.out.println("请输入你猜测的数字 ： ");
int g = sc.nextInt();
if (g > n) {
System.out.println("抱歉，您猜测的数字太大了.请重试");
} else if (g < n) {
System.out.println("抱歉，您猜测的数字太小了.请重试");
} else {
System.out.println("恭喜你，猜对了");
break;
}
System.out.println("您还有" + (10 - i) + "次机会");
}
System.out.println("游戏结束了！");
}
}
第四章.Arraylist类
1.创建方法
package day32;
import java.util.ArrayList;
public class Demo07 {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<String>();
list.add("唐僧");
list.add("孙悟空");
list.add("猪八戒");
list.add("沙僧");
System.out.println(list);
}
}
运行结果:
[唐僧, 孙悟空, 猪八戒, 沙僧]
2.Arraylist类的常用方法
package day32;
import java.util.ArrayList;
public class Demo08 {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<>();
boolean b = list.add("柳岩");
System.out.println("添加的动作是否成功 : " + b);
list.add("范冰冰");
list.add("刘亦菲");
list.add("鞠婧祎");
System.out.println(list);
String s1 = list.get(2);
System.out.println("第二号索引值的位置:" + s1);
String s = list.remove(1);
System.out.println("删除的人是:" + s);
System.out.println(list);
int i = list.size();
System.out.println("集合的长度为:" + i);
}
}
运行结果:
添加的动作是否成功 : true
[柳岩, 范冰冰, 刘亦菲, 鞠婧祎]
第二号索引值的位置:刘亦菲
删除的人是:范冰冰
[柳岩, 刘亦菲, 鞠婧祎]
集合的长度为:3
3.Arraylist集合的遍历
package day32;
import java.util.ArrayList;
public class Demo09 {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<>();
list.add("范冰冰");
list.add("刘亦菲");
list.add("鞠婧祎");
for (int i = 0; i < list.size(); i++) {
System.out.println(list.get(i));
}
}
}
运行结果:
范冰冰
刘亦菲
鞠婧祎4.Arraylist集合储存基本数据类型
package day32;
import java.util.ArrayList;
public class Demo10 {
public static void main(String[] args) {
ArrayList<Integer> arr = new ArrayList<>();
arr.add(100);
arr.add(360);
arr.add(521);
Integer i = arr.get(2);
System.out.println(i);
}
}
运行结果:
521
5.练习
(1)存储随机数字
package day32;
import java.util.ArrayList;
import java.util.Random;
public class Demo11 {
public static void main(String[] args) {
ArrayList<Integer> arr = new ArrayList<>();
Random r = new Random();
for (int j = 0; j < 6; j++) {
int num = r.nextInt(33) + 1;
arr.add(num);
}
for (int i = 0; i < arr.size(); i++) {
System.out.println(arr.get(i));
}
}
}
(2)存储自定义变量
package day32;
import java.util.ArrayList;
public class Demo12 {
public static void main(String[] args) {
ArrayList<Student> list = new ArrayList<>();
Student one = new Student("小龙女", 20);
Student two = new Student("杨过", 18);
Student three = new Student("郭靖", 38);
Student four = new Student("黄蓉", 39);
list.add(one);
list.add(two);
list.add(three);
list.add(four);
for (int i = 0; i < list.size(); i++) {
Student stu = list.get(i);
System.out.println("姓名是:" + stu.getName() + ", 年龄是:" + stu.getAge());
}
}
}
(3)按指定格式遍历集合字符串
package day32;
import java.util.ArrayList;
public class Demo13 {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<>();
list.add("东海龙王");
list.add("西海龙王");
list.add("南海龙王");
list.add("北海龙王");
System.out.println(list);
System.out.println("======================");
printArraylist(list);
}
public static void printArraylist(ArrayList<String> list) {
System.out.print("{");
for (int i = 0; i < list.size(); i++) {
String name = list.get(i);
if (i == list.size() - 1) {
System.out.print(name + "}");
} else {
System.out.print(name + "@");
}
}
}
}
(4)筛选集合中的随机数
package day32;
import java.util.ArrayList;
import java.util.Random;
public class Demo14 {
public static void main(String[] args) {
ArrayList<Integer> bigList = new ArrayList<>();
Random r = new Random();
for (int i = 0; i < 20; i++) {
int num = r.nextInt(100);
bigList.add(num);
}
ArrayList<Integer> smallList = getSmallList(bigList);
System.out.println("偶数的个数为 ： " + smallList.size() + "个");
for (int i = 0; i < smallList.size(); i++) {
System.out.println(smallList.get(i));
}
}
public static ArrayList<Integer> getSmallList(ArrayList<Integer> bigList) {
ArrayList<Integer> smallList = new ArrayList<>();
for (int j = 0; j < bigList.size(); j++) {
int num = bigList.get(j);
if (num % 2 == 0) {
smallList.add(num);
}
}
return smallList;
}
}
