java基础 -- 流程控制语句

亦凉 2023-06-13 06:11 21阅读 0赞

## java基础 – 流程控制语句 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDU1MDQ5MA_size_16_color_FFFFFF_t_70]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDU1MDQ5MA_size_16_color_FFFFFF_t_70 1]

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## IF ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDU1MDQ5MA_size_16_color_FFFFFF_t_70 2]

if (条件表达式) { 
        语句块;
    }

![在这里插入图片描述][20191114161906495.png]

--------------------

## 代码演示 ##

public static void main(String[] args) { 
        System.out.println("请输入一个数字：");
        Scanner input = new Scanner(System.in);
        int num = input.nextInt(); // 接收键盘输入数据
        // 判断用户输入的数据是否大于100
        if (num > 100) { 
            System.out.println("输入的数字大于100");
        }
        // 判断用户输入的数据是否等于100
        if (num == 100) { 
            System.out.println("输入的数字等于100");
        }
        // 判断用户输入的数据是否小于100
        if (num < 100) { 
            System.out.println("输入的数字小于100");
        }
    }

public static void main(String[] args) { 
        int num1 = 50;
        int num2 = 34;
        if (num1 > num2) { 
            System.out.println("num1大于num2");
        }
        if (num1 == num2) { 
            System.out.println("num2等于num2");
        }
        if (num1 < num2) { 
            System.out.println("num1小于num2");
        }
    }

public static void main(String[] args) { 
        String username = "admin"; // 用户名
        String userpass = "123456"; // 密码
        String code = "0000"; // 验证码
        if (username != "admin" && userpass != "123456" && code != "0000") { 
            System.out.println("登录失败！");
            System.out.println("异常！");
        }
    }

--------------------

## if-else 结构 ##

格式

if (表达式) { 
        语句块1;
    } else { 
        语句块2;
    }

执行流程

![在这里插入图片描述][20191114162636463.png]

--------------------

## 代码演示 ##

public static void main(String[] args) { 
        int num1 = 50;
        int num2 = 34;
        // 如果num1等于num2
        if (num1 == num2) { 
            System.out.println("num1等于num2");
        }
        // 如果num1大于num2
        if (num1 > num2) { 
            System.out.println("num1大于num2");
        } else { 
            // 否则就是num1小于num2
            System.out.println("num1小于num2");
        }
    }

--------------------

## 多条件 if-else-if 语句 ##

格式

if(表达式1) { 
        语句块1;
    } else if(表达式2) { 
        语句块2;
    ...
    } else if(表达式n) { 
        语句块n;
    } else { 
        语句块n+1;
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDU1MDQ5MA_size_16_color_FFFFFF_t_70 3]

--------------------

## 实例代码 ##

public static void main(String[] args) { 
        int num1 = 50;
        int num2 = 34;
        if (num1 == num2) {  // 如果num1等于num2
            System.out.println("num1等于num2");
        } else if (num1 > num2) {  // 如果num1大于num2
            System.out.println("num1大于num2");
        } else {  // 否则就是小于
            System.out.println("num1小于num2");
        }
    }

public static void main(String[] args) { 
        System.out.println("请输入考试成绩：");
        Scanner input = new Scanner(System.in);
        int score = input.nextInt(); // 接收键盘输入数据
        if (score >= 90) {  // 考试成绩>=90
            System.out.println("优秀");
        } else if (score >= 80) {  // 90>考试成绩>=80
            System.out.println("良好");
        } else if (score >= 60) {  // 80>考试成绩>=60
            System.out.println("中等");
        } else {  // 考试成绩<60
            System.out.println("差");
        }
    }

--------------------

## 嵌套 if 的使用 ##

格式

if(表达式1) { 
        if(表达式2) { 
            语句块1;
        } else { 
            语句块2;
        }
    } else { 
        if(表达式3) { 
            语句块3;
        } else if(表达式4) { 
            语句块4;
        } else { 
            if(表达式n) { 
                语句块n;
            } else { 
                语句块n+1;
            }
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDU1MDQ5MA_size_16_color_FFFFFF_t_70 4]

--------------------

## 实例代码 ##

public static void main(String[] args) { 
            Scanner sc = new Scanner(System.in);
            System.out.println("请输入出行的月份：");
            int month = sc.nextInt();
            System.out.println("选择头等舱还是经济舱？数字1为头等舱，数字2为经济舱");
            int kind = sc.nextInt();
            double result = 60000; // 原始价格
            // 旺季的票价计算
            if (month <= 11 && month >= 4) { 
                if (kind == 1) {  // 旺季头等舱
                    result = result * 0.9;
                } else if (kind == 2) {  // 旺季经济舱
                    result = result * 0.8;
                } else { 
                    System.out.println("选择种类有误，请重新输入！");
                }
            }
            // 淡季的票价计算
            else if ((month >= 1 && month <= 3) || month == 12) { 
                if (kind == 1) {  // 淡季头等舱
                    result = result * 0.5;
                } else if (kind == 2) {  // 淡季经济舱
                    result = result * 0.4;
                } else { 
                    System.out.println("选择种类有误，请重新输入！");
                }
            } else { 
                System.out.println("日期选择有误，请重新输入！");
            }
            System.out.println("您选择的机票价格为：" + result);
        }
    }

--------------------

## switch ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDU1MDQ5MA_size_16_color_FFFFFF_t_70 5]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDU1MDQ5MA_size_16_color_FFFFFF_t_70 6]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDU1MDQ5MA_size_16_color_FFFFFF_t_70 7]  
格式

switch(表达式) { 
        case 值1:
            语句块1;
            break;
        case 值2:
            语句块2;
            break;
        …
        case 值n:
            语句块n;
            break;
        default:
            语句块n+1;
        break;
    }

--------------------

## 实例代码 ##

public static void main(String[] args) { 
        System.out.println("请输入座位号码：");
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        switch (num) { 
        case 8:
            System.out.println("恭喜你，获得了三等奖！");
            break;
        case 88:
            System.out.println("恭喜你，获得了二等奖！");
            break;
        case 888:
            System.out.println("恭喜你，获得了一等奖！");
            break;
        default:
            System.out.println("谢谢参与！");
            break;
        }
    }

--------------------

## 区别 ##

--------------------

## switch实现计算星座功能 ##

public static void main(String[] args) { 
        System.out.println("请输入您的出生年月（如 0123 表示 1 月 23 日）：");
        Scanner sc = new Scanner(System.in);
        int monthday = sc.nextInt();
        int month = monthday/100;
        int day = monthday%100;
        String xingzuo = "";
        switch (month) { 
    　　    case 1:
                xingzuo = day<21?"摩羯座":"水瓶座";
                break;
    　　    case 2:
                xingzuo = day<20? "水瓶座":"双鱼座";
                break;
    　　    case 3:
                xingzuo = day<21?"双鱼座":"白羊座";
                break;
    　　    case 4:
                xingzuo = day<21?"白羊座":"金牛座";
                break;
            case 5:
                xingzuo = day<22?"金牛座":"双子座";
                break;
    　　    case 6:
                xingzuo = day<22?"双子座":"巨蟹座";
                break;
    　　    case 7:
                xingzuo = day<23?"巨蟹座":"狮子座";
                break;
    　　    case 8:
                xingzuo = day<24?"狮子座":"处女座";
                break;
    　　    case 9:
                xingzuo = day<24?"处女座":"天秤座";
                break;
    　　    case 10:
                xingzuo = day<24?"天秤座":"天蝎座";
                break;
    　　    case 11:
                xingzuo = day<23?"天蝎座":"射手座";
                break;
    　　    case 12:
                xingzuo = day<22?"射手座":"摩羯座";
                break;
        }
        System.out.println("您的星座是：" +xingzuo);
    }

## if-else 实现计算星座功能 ##

public static void main(String[] args) { 
        System.out.println("请输入您的出生年月（如 0123 表示 1 月 23 日）：");
        Scanner sc = new Scanner(System.in);
        int monthday = sc.nextInt();
        int month = monthday / 100;
        int day = monthday % 100;
        String xingzuo = "";
    
        if (month == 1) { 
            if (day < 21) { 
                xingzuo = "摩羯座";
            } else { 
                xingzuo = "水瓶座";
            }
        } else if (month == 2) { 
            if (day < 20) { 
                xingzuo = "水瓶座";
            } else { 
                xingzuo = "双鱼座";
            }
        } else if (month == 3) { 
            if (day < 21) { 
                xingzuo = "双鱼座";
            } else { 
                xingzuo = "白羊座";
            }
        } else if (month == 4) { 
            if (day < 21) { 
                xingzuo = "白羊座";
            } else { 
                xingzuo = "金牛座";
            }
        } else if (month == 5) { 
            if (day < 22) { 
                xingzuo = "金牛座";
            } else { 
                xingzuo = "双子座";
            }
        } else if (month == 6) { 
            if (day < 22) { 
                xingzuo = "双子座";
            } else { 
                xingzuo = "巨蟹座";
            }
        } else if (month == 7) { 
            if (day < 23) { 
                xingzuo = "巨蟹座";
            } else { 
                xingzuo = "狮子座";
            }
        } else if (month == 8) { 
            if (day < 24) { 
                xingzuo = "狮子座";
            } else { 
                xingzuo = "处女座";
            }
        } else if (month == 9) { 
            if (day < 24) { 
                xingzuo = "处女座";
            } else { 
                xingzuo = "天秤座";
            }
        } else if (month == 10) { 
            if (day < 24) { 
                xingzuo = "天秤座";
            } else { 
                xingzuo = "天蝎座";
            }
        } else if (month == 11) { 
            if (day < 23) { 
                xingzuo = "天蝎座";
            } else { 
                xingzuo = "射手座";
            }
        } else if (month == 12) { 
            if (day < 22) { 
                xingzuo = "射手座";
            } else { 
                xingzuo = "摩羯座";
            }
        }
        System.out.println("您的星座是：" + xingzuo);
    }

--------------------

综合上诉，效率方面Switch显得要快一些，但是从实用性来说 如果否则，相对来说更加语义通用

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[20191114161906495.png]: https://img-blog.csdnimg.cn/20191114161906495.png
[20191114162636463.png]: https://img-blog.csdnimg.cn/20191114162636463.png
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