1. Sequence structure
2. Selection structure
//import java.util.Scanner;
public class ifelse {
public static void main(String [] args){
// Scanner input = new Scanner(System.in);
/**
System.out.println("请输入成绩:");
int score = input.nextInt();
if(score>=90){
System.out.print("A级");
}
else if(score>=80){
System.out.print("B级");
}
else {
System.out.print("C级");
}
//运动会
* System.out.println();
double time = input.nextInt();
String gender = input.next();//=null;
if(time<10){
if(gender=="男"){//("男".equals(gender))
System.out.print("");
}else if(gender.equals("")){
System.out.print("");
}
}else{
System.out.print("淘汰");
}
//根据用户输入星期、气温、天气进行判断
System.out.print("请输入今天星期几：");
int week = input.nextInt();
if(0<week&week<=7){
if(week==6||week==7){
System.out.print("请输入今天的温度：");
double temperature = input.nextInt();
if(temperature>=30){
System.out.print("今天去游泳。");
}else{
System.out.print("今天去爬山。");
}
}else{
System.out.print("请输入今天的天气：");
String day = input.next();
if(day.equals("晴")){
System.out.print("今天谈业务。");
}else{
System.out.print("今天上网查资料。");
}
}
}else{
System.out.print("一周只有七天，请输入1-7之间的数字。");
}
//switch 判断
int score = input.nextInt();
switch(score/10){
case 10:
System.out.print("A级");
break;
default:
System.out.print("E级");
}
//根据用户输入年份、月份进行判断
System.out.print("请输入年份：");
int year = input.nextInt();
System.out.print("请输入月份:");
int month = input.nextInt();
switch(month){
case 2:
if(year%4==0&year%100!=0&year%400==0){
System.out.print("28days");
}else{
System.out.print("29days");
}break;
case 4:
case 6:
case 9:
case 11:
System.out.print("30days");
break;
default:
System.out.print("31days");
}
//100求和
int i = 1;
int sum = 0 ;
while(i<=100){
sum = sum + i ;
i++;
}
System.out.println("sum is :"+sum);
//**/
/*
int i=3;
while(i>=0){
System.out.println("请输入用户名：");
String user = input.next();
System.out.println("请输入密码：");
int password = input.nextInt();
if("zhxj".equals(user)&&password==123456){
System.out.print("欢迎进入系统！");
break;
}else{
System.out.print("输入错误，您还有"+i+"次机会！");
}
i--;
}*/
//System.out.print("请输入0-9之间的数字：");
/*System.out.print("请输入一个随机数字：");
int result = (int)(Math.random()*10);
int num = input.nextInt();
while(result!=num){
if(result<num){
System.out.println("不好意思答错了！");
System.out.println("您猜大了！");
}else if(result>num){
System.out.println("不好意思答错了！");
System.out.println("您猜小了！");
}
System.out.println("请重新输入一个随机数字：");
num = input.nextInt();
}
System.out.println("恭喜您答对了！");
/*
* public static void main(String[] args) {
//System.out.print("请输入0-9之间的数字：");
//Scanner input = new Scanner(System.in);
int i = 1;
int sum =0 ;
do{
sum = sum + i;
i++;
}while(i <= 100);
System.out.print("Sum is:" + sum);
}
*/
/*
* int i;
do{
System.out.println("************欢迎光临QQ登陆页面***********");
System.out.println("1、注册");
System.out.println("2、登录");
System.out.println("3、退出");
System.out.println("您的输入是：");
i = input.nextInt();
}while(i!=3);
System.out.println("************再见！***********");
int sum = 0;
for(int i = 1;i <= 100;i ++){
sum += i;
}
System.out.println("SUM=" + sum);
*/
/*System.out.print("请输入学生的姓名：");
String name = input.next();
int sum = 0;
for(int i = 1; i<=5;i++){
System.out.println("请输入第"+i+"门的成绩：");
int score = input.nextInt();
sum = sum + score;
}
System.out.println(name+"的平均分是："+sum/5);
String y ;
do{
System.out.print("请输入学生的姓名：");
String name = input.next();
int sum = 0;
for(int i = 1; i<=5;i++){
System.out.println("请输入5门功课中第"+i+"门的成绩：");
int score = input.nextInt();
sum = sum + score;
}
System.out.println(name+"的平均分是："+sum/5);
System.out.print("继续输入吗？(y/n)");
y = input.next();
}while("y".equals(y));
System.out.print("成绩录入结束！");
for(int i=1;i<=10;i++){
if(i % 4 == 0){
break;
}
System.out.print(i);
}
System.out.print("循环结束。");
*/
//百元百鸡
for(int n=0;n<100/5;n++){//公鸡购买数量；
for(int m=0;m<100/3;m++){//母鸡购买数量；
int l = 100-n-m;//购买小鸡的数量；
if((n*5+m*3+l/3)==100&&(l%3==0)){
System.out.println(n+","+m+","+l);
}
}
}
}
}
3. Loop structure
for loop
One hundred yuan buys 100 chickens
public class ifelse {
public static void main(String [] args){
for(int n=0;n<100/5;n++){ //公鸡购买数量；
for(int m=0;m<100/3;m++){ //母鸡购买数量；
int l = 100-n-m; //购买小鸡的数量；
if((n*5+m*3+l/3)==100&&(l%3==0)){
System.out.println(n+","+m+","+l);
}
}
}
}
}Result verification:
0,25,75 4,18,78 8,11,81 12,4,84
Example 2:
//Find all prime numbers in 3-100: prime numbers can only be divisible by 1 and themselves
public class sum {
public static void main(String [] args){
//Scanner input = new Scanner(System.in);
//求3-100中的所有素数：素数只能被1和自己整除的数字
for(int b=2;b<100;b++){
for(int a=2;a<=b;a++){
if(b%a==0){
if(a==b){
System.out.print(b+" ");
}
break;
}
}
}
}
}Result verification :
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
Parameter passing example:
public class calc {
public void calc1(int num){
num = num + 1;
}
public void calc2(students stu){
stu.setAge(stu.getAge()+1);
}
}
##
public class calc {
public void calc1(int num){
num = num + 1;
}
public void calc2(students stu){
stu.setAge(stu.getAge()+1);
}
}public class students{
//students类的属性
private String name;
private int age;
private String gender;
//students类的构造方法
public students(){
//空方法，默认值
}
public students(String name,int age,String gender){
//students类的构造方法
this.name = name ;
this.age = age ;
this.gender = gender ;
}
//students的get方法获取属性值
public String getName(){
return this.name;
}
public int getAge(){
return this.age;
}
public String getGender(){
return this.gender;
}
//students的set方法对属性进行赋值
public void setName(String name){
this.name = name ;
}
public void setAge(int age){
//对age进行范围圈定和判断
if(age>45 || age<15){
this.age=18;
}else{
this.age = age ;
}
}
public void setGender(String gender){
this.gender = gender ;
}
}public class studentsDemo {
public static void main(String[] args) {
//实例化对象
students st = new students() ;
// st.name="小明";
// st.age=12;
// st.gender="男";
// System.out.println(st.name+"\n"+st.age+"\n"+st.gender+"\n");
// st.setName("小虎");
// st.setAge(14);
// st.setGender("男");
// System.out.println(st.getName()+"\n"+st.getAge()+"\n"+st.getGender()+"\n");
//1、定义对象数组
students[] arrs = new students [3];
//2、实例化对象
students s1 = new students("张三",15,"男");
students s2 = new students("李四",20,"女");
students s3 = new students("王五",31,"男");
//3、将对象放入对象数组
arrs[0] = s1;
arrs[1] = s2;
arrs[2] = s3;
//students[]arrs={s1,s2,s3};
//students[]arrs={new students("张三",15,"男"),
//new students("李四",20,"女"),
//new students("王五",31,"男")};
//4、遍历输出对象数组里的对象
for(students i : arrs){
System.out.println(i.getName()+"\t"+i.getAge()+"\t"+i.getGender()+"\t");
}
System.out.println("\n");
for(int i = 0; i < arrs.length; i++){
System.out.println(arrs[i].getName()+"\t"+arrs[i].getAge()+"\t"+arrs[i].getGender()+"\t");
}
}
}
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