1.使用if语句进行最基本的条件测试;
2.测试一个值大于还是小于另一个值;
3.测试两个值是否相等;
4.使用与if语句对应的else语句;
5.组合多个条件测试;
6.使用switch语句进行复杂的条件测试;
7.使用三元运算符创建测试;
程序Game:if语句的初步使用 1 package com.jsample;
2
3 public class Game {
4 public static void main(String[] args){
5 int total = 0;
6 int score = 7;
7 if(score == 7){
8 System.out.println("You score a touchdown!");
9 }
10 if(score == 3){
11 System.out.println("You kick a field goal!");
12 }
13 total = total + score;
14 System.out.println("Total score: " + total);
15 }
16 }
View Code
输出: You score a touchdown!
Total score: 7
程序Commodity:使用switch语句来购买或销售东西 1 package com.jsample;
2
3 public class Commmodity {
4 public static void main(String[] args){
5 String command = "BUY";//指令被设定为“BUY”
6 int balance = 550;
7 int quantity = 42;
8
9 switch (command) {
10 case "BUY":
11 quantity += 5;
12 balance -= 20;
13 break;
14 case "SELL":
15 quantity -= 5;
16 balance += 15;
17 }
18 System.out.println("Balance: " + balance + "\n"
19 + "Quantity: " + quantity);
20 }
21 }
View Code
输出: Balance: 530
Quantity: 47
程序Clock:使用java内置的计时功能,跟踪当前的日期和时间,并将信息用一句话显示出来 1 package com.jsample;
2
3 import java.time.*; //让程序能够使用类java.time.LocalDateTime,它用于跟踪当前的日期和时间
4 import java.time.temporal.*;//让程序能够使用java.time.temporalfield.ChronoField
5
6 public class Clock {//开始Clock程序及其main()语句块
7 public static void main(String[] args){
8 //get current time and date
9 LocalDateTime now = LocalDateTime.now();//创建一个名为now的LocalDateTime对象,该对象包含系统的当前日期和时间
10 int hour = now.get(ChronoField.HOUR_OF_DAY);//创建变量hour,month,day,year,这些变量的值来自LocalDateTime对象
11 int minute = now.get(ChronoField.MINUTE_OF_HOUR);
12 int month = now.get(ChronoField.MONTH_OF_YEAR);
13 int day = now.get(ChronoField.DAY_OF_MONTH);
14 int year = now.get(ChronoField.YEAR);
15
16 //display greeting
17 if(hour < 12){//显示三个问候语之一,显示的内容取决于变量hour的值
18 System.out.println("Good morning.\n");
19 }else if (hour < 17){
20 System.out.println("Good afternoon.\n");
21 }else {
22 System.out.println("Good evening");
23 }
24
25 //begin time message by showing the minutes
26 System.out.print("It's");//根据变量minute的值来显示具体的分钟数
27 if (minute != 0){
28 System.out.print(" " + minute + " ");
29 System.out.print((minute != 1) ? "minutes" : "minute");
30 System.out.print(" past");
31 }
32
33 //display the hour
34 System.out.print(" ");//显示十二小时制下的hour值
35 System.out.print((hour > 12) ? (hour - 12) : hour);
36 System.out.print(" o'clock on ");
37
38 //display the name of the month
39 switch (month){//根据变量month的值来显示不同的月份名称
40 case 1:System.out.print("January");break;
41 case 2:System.out.print("February");break;
42 case 3:System.out.print("March");break;
43 case 4:System.out.print("April");break;
44 case 5:System.out.print("May");break;
45 case 6:System.out.print("June");break;
46 case 7:System.out.print("July");break;
47 case 8:System.out.print("August");break;
48 case 9:System.out.print("September");break;
49 case 10:System.out.print("October");break;
50 case 11:System.out.print("November");break;
51 case 12:System.out.print("December");break;
52 }
53
54 //display the date and year
55 System.out.println(" " + day + "," + year + ".");//显示当前的日期和年份
56 }//结束main()语句块
57 }//结束整个clock程序
View Code
输出: Good morning. It's 15 minutes past 9 o'clock on March 16,2018.
程序GradeGame:存储用户输入的成绩(0-100),自动分等级并输出评语(分别以if语句和switch语句实现) 1 package com.jsample;
2
3 public class GradeGame {
4 public static void main(String[] args){
5 int grade = Integer.parseInt(args[0]);
6 char gpa = 'E';
7
8 if (grade > 80)
9 {
10 System.out.println("Aerfect");
11 gpa = 'A';
12 }
13 else if (grade > 60)
14 {
15 System.out.println("B Good");
16 gpa = 'B';
17 }
18 else if (grade > 40)
19 {
20 System.out.println("C Not bad");
21 gpa = 'C';
22 }
23 else if (grade > 20)
24 {
25 System.out.println("D You still have lots more to work on");
26 gpa = 'D';
27 }
28 else
29 {
30 System.out.println("F Not even wrong");
31 gpa = 'F';
32 }
33
34 switch (gpa){
35 case 'A':System.out.println("A:Perfect");break;
36 case 'B':System.out.println("B Good");break;
37 case 'C':System.out.println("C Not bad");break;
38 case 'D':System.out.println("D You still have lots more to work on");break;
39 case 'F':System.out.println("F Not even wrong");break;
40 default:System.out.println("Who's your daddy");break;
41 }
42 }
43 }
View Code
输入: 65 输出: B Good
B Good
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