Java基础语法2

# 顺序结构

程序从上到下依次地执行，中间没有任何判断和跳转。

        System.out.println("程序开始");

        System.out.println("起床");
        System.out.println("洗漱");
        System.out.println("开车");
        System.out.println("工作");
        System.out.println("下班");
        System.out.println("睡觉");

        System.out.println("程序结束");

分支结构

if

        int age = 34234;

        if (age < 0 || age >= 150) {
            System.out.println("妖怪！");
        } else {
            if (age >= 60) {
                System.out.println("老年");
            } else if (age >= 40) {
                System.out.println("壮年");
            } else if (age >= 20) {
                System.out.println("青年");
            } else {
                System.out.println("未成年");
            }
        }

switch

        String color = "green";

        switch (color) {
            case "red":
                System.out.println("红色");
                break;	
            case "yellow":
                System.out.println("黄色");
                break;
            case "green":
                System.out.println("绿色");
                break;
            case "white":
                System.out.println("白色");
                break;
            default:
                System.out.println("花色");
                break;
        }

总结：if和switch很像，具体什么场景使用什么语句？

• 判断的值不多或者是固定的值，使用switch
• 对于区间判断，使用if

---

Scanner

        import java.util.Scanner;//1.导包

        //2.创建扫描器对象
        Scanner sc = new Scanner(System.in);

        System.out.print("输入你名字:");
        String name = sc.next();

        System.out.print("输入你年龄:");
        int age = sc.nextInt();

        System.out.print("输入你的性别:");
        char gender = sc.next().charAt(0);

        System.out.print("输入你的成绩:");
        double score = sc.nextDouble();

        System.out.println("名字 = " + name);
        System.out.println("年龄 = " + age);
        System.out.println("性别 = " + gender);
        System.out.println("成绩 = " + score);

循环结构

while

        int i = 1;
        while (i<=5){
            System.out.println("hi");
            i++;
        }

do while

        int i = 1;
        do {
            System.out.println("hi");
            i++;
        } while (i <= 5);

for

        for (int i = 1; i <= 5; i++) {
            System.out.println("hi");
        }

总结：while 和 do-while 的区别?

• while：先判断循环条件，再执行循环体
• do-while：先执行循环体，再判断循环条件，至少执行一次

---

特殊流程控制

break

        for (int i = 1; i <= 40; i++) {
            if (i == 13) {
                break;//跳出循环
            }
            System.out.println(i);
        }

---

continue

        for (int i = 1; i <= 40; i++) {
            if (i == 13) {
                continue;//跳过当前循环，执行下次循环
            }
            System.out.println(i);
        }