Java习题练习（一）
输出[1,100]内所有的质数，并统计
System.out.println(1);
int sum = 0;
for(int a = 2; a < 101; a++) {
int b = 2;
while (b < a) {
if (a % b == 0) {
break;
}
b++;
}
if (a == b) {
System.out.println(b);
sum += 1;
}
}
System.out.println("在[1,100]内，质数总数为：" + (sum+1));
求斐波拉契数列的第十个数字大小
public static void main(String[] args) {
int n =10;
System.out.println(func(n));
}
private static int func(int n) {
if (n == 1 || n== 2) {
return 1;
}
else {
return func(n-1) + func(n-2);
}
} for(int i = 100; i < 1001; i++) {
int a = i / 100;
int b = i / 10 % 10;
int c = i % 10;
if (i == a*a*a + b*b*b +c*c*c) {
System.out.println(i);
}
}
不是题目，熟悉一下方法调用
public static void main(String[] args) {
String[] names = new String[8];
getName(names);
printNames(names);
String name = rdnames(names);
System.out.println("___________________");
System.out.println(name);
}
public static void getName(String[] names) {
names[0] = "A";
names[1] = "B";
names[2] = "C";
names[3] = "D";
names[4] = "E";
names[5] = "F";
names[6] = "G";
names[7] = "H";
}
public static void printNames(String[] names) {
for(int i = 0; i < names.length; i++) {
System.out.println(names[i]);
}
}
public static String rdnames(String[] names) {
int index = new Random().nextInt(names.length);
return names[index];
}
集合里面，随机数生成：
public static void main(String[] args) {
ArrayList array = new ArrayList();
add(array);
for( int i = 0; i < array.size(); i++) {
studentName s = array.get(i); //返回的是类！
System.out.println(s.name + " " + s.age);
}
Random rd = new Random();
studentName m = array.get(rd.nextInt(array.size()));
System.out.println(m.name + " " + m.age);
}
public static void add(ArrayList array) {
studentName sn1 = new studentName();
studentName sn2 = new studentName();
studentName sn3 = new studentName();
studentName sn4 = new studentName();
studentName sn5 = new studentName();
sn1.name = "yi";
sn1.age = 1;
sn2.name = "er";
sn2.age = 2;
sn3.name = "san";
sn3.age = 3;
sn4.name = "si";
sn4.age = 4;
sn5.name = "wu";
sn5.age = 5;
array.add(sn1);
array.add(sn2);
array.add(sn3);
array.add(sn4);
array.add(sn5);
}
斗地主打牌
public class Doudizhu {
public static void main(String[] args) {
//1. 组合牌
//创建Map集合,键是编号,值是牌
HashMap pooker = new HashMap();
//创建List集合,存储编号
ArrayList pookerNumber = new ArrayList();
//定义出13个点数的数组
String[] numbers = {"2","A","K","Q","J","10","9","8","7","6","5","4","3"};
//定义4个花色数组
String[] colors = {"♠","♥","♣","♦"};
//定义整数变量,作为键出现
int index = 2;
//遍历数组,花色+点数的组合,存储到Map集合
for(String number : numbers){
for(String color : colors){
pooker.put(index, color+number);
pookerNumber.add(index);
index++;
}
}
//存储大王,和小王
pooker.put(0, "大王");
pookerNumber.add(0);
pooker.put(1, "小王");
pookerNumber.add(1);
//洗牌,将牌的编号打乱
Collections.shuffle(pookerNumber);
//发牌功能,将牌编号,发给玩家集合,底牌集合
ArrayList player1 = new ArrayList();
ArrayList player2 = new ArrayList();
ArrayList player3 = new ArrayList();
ArrayList bottom = new ArrayList();
//发牌采用的是集合索引%3
for(int i = 0 ; i < pookerNumber.size() ; i++){
//先将底牌做好
if(i < 3){
//存到底牌去
bottom.add( pookerNumber.get(i));
//对索引%3判断
}else if(i % 3 == 0){
//索引上的编号,发给玩家1
player1.add( pookerNumber.get(i) );
}else if( i % 3 == 1){
//索引上的编号,发给玩家2
player2.add( pookerNumber.get(i) );
}else if( i % 3 == 2){
//索引上的编号,发给玩家3
player3.add( pookerNumber.get(i) );
}
}
//对玩家手中的编号排序
Collections.sort(player1);
Collections.sort(player2);
Collections.sort(player3);
//看牌,将玩家手中的编号,到Map集合中查找,根据键找值
//定义方法实现
look("A",player1,pooker);
look("B",player2,pooker);
look("C",player3,pooker);
look("底牌",bottom,pooker);
}
public static void look(String name,ArrayList player,HashMap pooker){
//遍历ArrayList集合,获取元素,作为键,到集合Map中找值
System.out.print(name+" ");
for(Integer key : player){
String value = pooker.get(key);
System.out.print(value+" ");
}
System.out.println();
}
}