011 Java选择结构

选择结构

顺序结构

Java基本结构为顺序结构，无特别指出，将按照顺序一句一句执行

public class Order {
    public static void main(String[] args) {
        System.out.println("1");
        System.out.println("2");
        System.out.println("3");
    }
}

选择结构

if选择

if多选

if嵌套

public class Choice {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩：");
        int achievement = scanner.nextInt();
        if (achievement <= 100 && achievement >= 0) {
            //if可以以任何方式嵌套
            if (achievement == 100) {
                System.out.println("满分");
            } else if (achievement < 100 && achievement >= 90) {
                System.out.println("A");
            } else if (achievement < 90 && achievement >= 80) {
                System.out.println("B");
            } else if (achievement < 80 && achievement >= 70) {
                System.out.println("C");
            } else if (achievement < 70 && achievement >= 60) {
                System.out.println("D");
            } else {
                System.out.println("不及格");
            }
        } else {
            System.out.println("输入不合法");
        }
        scanner.close();
    }
}

switch多选

JDK7开始支持String类型
case不加break会产生穿透现象

public class MultipleChoice {
    public static void main(String[] args) {
        char a='A';
        switch (a){
            case 'A':
                System.out.println("A");
                break;
            case 'B':
                System.out.println("B");
                break;
            case 'C':
                System.out.println("C");
                break;
            default:
                System.out.println("default");
        }
    }
}

case后不跟break时会在判断成功后把后面的全部执行