=90"/> =90">
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); } }Object array:
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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