Java自动化测试(循环/条件控制语句 预习3)

for循环

格式

for(初始化值1;循环终止条件2;循环体执行后的语句4){
    循环体3;
}

for (int i = 0; i <= 10; i++) {
    System.out.println(i);
}

流程

初始化值1->循环终止条件2「true」->循环体3->循环体执行后的语句4 ->循环终止条件2「true」->循环体3->循环体执行后的语句4->…循环终止条件2「false」-> 循环结束

增强for循环

for(内部元素类型 变量名;集合){}

普通方式实现

int[] arr = {100, 24, 90, 78};
for (int i = 0; i < arr.length; i++) {
  System.out.println(arr[i]);
}

增强方式实现

• 优点：代码少
• 缺点：不能直接获取索引

for (int i : arr) {
    System.out.println(i);
}

求和

package com.zhongxin.loop;

public class ForDemo2 {
    public static void main(String[] args) {
        int sum = 0;
        for (int i = 0; i <= 10; i++) {
            sum += i;
        }
        System.out.println(sum);
    }
}

while循环

package com.zhongxin.loop;

public class WhileDemo {
    public static void main(String[] args) {
        int i = 1;                  // 初始化语句1
        while (i <= 10) {           // 循环执行条件2
            System.out.println(i);  // 循环体3
            i++;                    // 循环体执行完毕之后的语句4
        }
    }
}

流程：1234->2(true)->34->2(true)->......->2(false)->循环结束

Do…While

至少会执行一次循环体，其他和while一样

package com.zhongxin.loop;

public class DoWhileDemo {
    public static void main(String[] args) {
        int i = 1;
        do {
            System.out.println(i);
            i++;
        } while (i <= 10);
    }
}

break

跳出整个循环

for (int i = 1; i <= 10; i++) {
    if (i == 3) {
        break;
    }
    System.out.println(i);
}
// 1
// 2

continue

结束本次循环,继续下次循环

package com.zhongxin.loop;

public class BreakContinueDemo {
    public static void main(String[] args) {
        for (int i = 1; i <= 10; i++) {
            if (i == 3) {
                continue;
            }
            System.out.println(i);
        }
    }
}
// 1
// 2
// 4
// 5
// 6
// 7
// 8
// 9
// 10

条件控制语句

• switch
• if … else
• if else if … else
• if … if … if

if

package com.zhongxin.ifdemo;

public class IFDemo {
    public static void main(String[] args) {
        int age = 17;
        if (age >= 18) {
            System.out.println("恭喜你成年了");
        }
        if (age >= 18) {
            System.out.println("可以访问本网站");
        }else{
            System.out.println("FBI WARNING!");
        }

        int score = 60;
        if (score == 100) {
            System.out.println("满分");
        }else if (score>=90){
            System.out.println("优秀");
        }else if (score>=60){
            System.out.println("及格");
        }else {
            System.out.println("不及格");
        }
    }
}

switch

优点

效率比if快

结束的条件

• switch
• 右大括号

变量类型

• <= int
• String
• 枚举

package com.zhongxin.ifdemo;

public class SwitchDemo {
    public static void main(String[] args) {
        int i = 1;
        switch (i) {
            case 1:
                System.out.println("1");
                break;
            case 2:
                System.out.println("2");
                break;
            default:
                System.out.println("未知");
                break;
        }
    }
}

不使用break 形成穿透

package com.zhongxin.ifdemo;

public class SwitchDemo2 {
    public static void main(String[] args) {
        int mouth = 12;
        switch (mouth) {
            case 3:
            case 4:
            case 5:
                System.out.println("春");
                break;
            case 6:
            case 7:
            case 8:
                System.out.println("夏");
                break;
            case 9:
            case 10:
            case 11:
                System.out.println("秋");
                break;
            case 12:
            case 1:
            case 2:
                System.out.println("冬");
                break;
            default:
                System.out.println("未知");
                break;
        }
    }
}

练习

打印

*
**
***
****
*****

package com.zhongxin.ifdemo;

public class Homework {
    public static void main(String[] args) {
        String start = "*";
        for (int i = 1; i < 6; i++) {
            for (int j = 0; j < i; j++) {
                System.out.print(start);
            }
            System.out.println("");
        }
    }
}

打印

    *  
   * * 
  * * *
 * * * *
* * * * *

package com.zhongxin.ifdemo;

public class Homework1 {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            for (int j = 0; j < 5 - i; j++) {
                System.out.print(" ");
            }
            for (int x = 1; x <= i * 2 - 1; x += 2) {
                System.out.print("* ");
            }
            System.out.println();
        }
    }
}