1、順序結構
2、選擇結構
//import java.util.Scanner;
public class ifelse {
public static void main(String [] args){
// Scanner input = new Scanner(System.in);
/**
System.out.println("請輸入成績:");
int score = input.nextInt();
if(score>=90){
System.out.print("A級");
}
else if(score>=80){
System.out.print("B級");
}
else {
System.out.print("C級");
}
//運動會
* 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");
}
//根據用戶輸入星期、氣溫、天氣進行判斷
System.out.print("請輸入今天星期幾：");
int week = input.nextInt();
if(0<week&week<=7){
if(week==6||week==7){
System.out.print("請輸入今天的溫度：");
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("請輸入今天的天氣：");
String day = input.next();
if(day.equals("晴")){
System.out.print("今天談業務。");
}else{
System.out.print("今天上網查資料。");
}
}
}else{
System.out.print("一週只有七天，請輸入1-7之間的數字。");
}
//switch 判斷
int score = input.nextInt();
switch(score/10){
case 10:
System.out.print("A級");
break;
default:
System.out.print("E級");
}
//根據用戶輸入年份、月份進行判斷
System.out.print("請輸入年份：");
int year = input.nextInt();
System.out.print("請輸入月份:");
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("請輸入用戶名：");
String user = input.next();
System.out.println("請輸入密碼：");
int password = input.nextInt();
if("zhxj".equals(user)&&password==123456){
System.out.print("歡迎進入系統！");
break;
}else{
System.out.print("輸入錯誤，您還有"+i+"次機會！");
}
i--;
}*/
//System.out.print("請輸入0-9之間的數字：");
/*System.out.print("請輸入一個隨機數字：");
int result = (int)(Math.random()*10);
int num = input.nextInt();
while(result!=num){
if(result<num){
System.out.println("不好意思答錯了！");
System.out.println("您猜大了！");
}else if(result>num){
System.out.println("不好意思答錯了！");
System.out.println("您猜小了！");
}
System.out.println("請重新輸入一個隨機數字：");
num = input.nextInt();
}
System.out.println("恭喜您答對了！");
/*
* public static void main(String[] args) {
//System.out.print("請輸入0-9之間的數字：");
//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("************歡迎光臨QQ登陸頁面***********");
System.out.println("1、註冊");
System.out.println("2、登錄");
System.out.println("3、退出");
System.out.println("您的輸入是：");
i = input.nextInt();
}while(i!=3);
System.out.println("************再見！***********");
int sum = 0;
for(int i = 1;i <= 100;i ++){
sum += i;
}
System.out.println("SUM=" + sum);
*/
/*System.out.print("請輸入學生的姓名：");
String name = input.next();
int sum = 0;
for(int i = 1; i<=5;i++){
System.out.println("請輸入第"+i+"門的成績：");
int score = input.nextInt();
sum = sum + score;
}
System.out.println(name+"的平均分是："+sum/5);
String y ;
do{
System.out.print("請輸入學生的姓名：");
String name = input.next();
int sum = 0;
for(int i = 1; i<=5;i++){
System.out.println("請輸入5門功課中第"+i+"門的成績：");
int score = input.nextInt();
sum = sum + score;
}
System.out.println(name+"的平均分是："+sum/5);
System.out.print("繼續輸入嗎？(y/n)");
y = input.next();
}while("y".equals(y));
System.out.print("成績錄入結束！");
for(int i=1;i<=10;i++){
if(i % 4 == 0){
break;
}
System.out.print(i);
}
System.out.print("循環結束。");
*/
//百元百雞
for(int n=0;n<100/5;n++){//公雞購買數量；
for(int m=0;m<100/3;m++){//母雞購買數量；
int l = 100-n-m;//購買小雞的數量；
if((n*5+m*3+l/3)==100&&(l%3==0)){
System.out.println(n+","+m+","+l);
}
}
}
}
}3、循環結構
for循環
練習
百元百雞
公雞一隻5元，母雞一隻3元，小雞三隻1元，一百元買一百隻雞，問各多少隻
提示
計算公雞、母雞的取值範圍（最多分別能買多少隻）
通過公雞、母雞判斷小雞的取值範圍
根據條件（公雞*5+母雞*3+小雞/3.0=100）進行計算
public class ifelse {
public static void main(String [] args){
for(int n=0;n<100/5;n++){ //公雞購買數量；
for(int m=0;m<100/3;m++){ //母雞購買數量；
int l = 100-n-m; //購買小雞的數量；
if((n*5+m*3+l/3)==100&&(l%3==0)){
System.out.println(n+","+m+","+l);
}
}
}
}
}結果驗證：
0,25,75
4,18,78
8,11,81
12,4,84
示例2：
//求3-100中的所有素數：素數只能被1和自己整除的數字
public class sum {
public static void main(String [] args){
//Scanner input = new Scanner(System.in);
//求3-100中的所有素數：素數只能被1和自己整除的數字
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;
}
}
}
}
}結果驗證：
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
傳參示例：
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);
}
} 對象數組：
public class students{
//students類的屬性
private String name;
private int age;
private String gender;
//students類的構造方法
public students(){
//空方法，默認值
}
public students(String name,int age,String gender){
//students類的構造方法
this.name = name ;
this.age = age ;
this.gender = gender ;
}
//students的get方法獲取屬性值
public String getName(){
return this.name;
}
public int getAge(){
return this.age;
}
public String getGender(){
return this.gender;
}
//students的set方法對屬性進行賦值
public void setName(String name){
this.name = name ;
}
public void setAge(int age){
//對age進行範圍圈定和判斷
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) {
//實例化對象
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、定義對象數組
students[] arrs = new students [3];
//2、實例化對象
students s1 = new students("張三",15,"男");
students s2 = new students("李四",20,"女");
students s3 = new students("王五",31,"男");
//3、將對象放入對象數組
arrs[0] = s1;
arrs[1] = s2;
arrs[2] = s3;
//students[]arrs={s1,s2,s3};
//students[]arrs={new students("張三",15,"男"),
//new students("李四",20,"女"),
//new students("王五",31,"男")};
//4、遍歷輸出對象數組裏的對象
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");
}
}
}