if语句

语法格式：

if(表达式){
    若干语句
}

                                                  

例：

​import java.util.Scanner;
public class Test1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        if(n%2==0){
            System.out.println("even");
        }
        if(n%2!=0){
            System.out.println("old");
        }
    }
}

if-else语句

if(表达式){
    若干语句
}else{
    若干语句
}

例：

import java.util.Scanner;

public class Test1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        if(n%2==0){
            System.out.println("even");
        }else{
            System.out.println("old");
        }
    }
}

if-else if-else 语句

if(表达式){
    若干语句
}else if(表达式){
    若干语句
}
...
else{
    若干语句
}

例：

import java.util.Scanner;

public class Test1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        if(n%3==0){
            System.out.println("YES");
        }else if(n%5==0){
            System.out.println("YES");
        }else{
            System.out.println("NO");
        }
    }
}

switch语句

JDK17之前：

switch(表达式){
    case 常量值1:
              若干语句
              break;
    case 常量值2:
              若干语句
              break;
    ...
    case 常量值n:
              若干语句
              break;
    default:
           若干语句
}

例：

                                   a*b mod c = (a mod c)*(b mod c)mod c

import java.util.Scanner;

public class Test1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        a %= 7;
        int ans = 1;
        for(int i=1;i<=b;i++){
            ans *= a;
            ans %= 7;
        }
        switch(ans){
            case 0:
                System.out.println("Sunday");
                break;
            case 1:
                System.out.println("Monday");
                break;
            case 2:
                System.out.println("Monday");
                break;
            case 3:
                System.out.println("Wednesday");
                break;
            case 4:
                System.out.println("Thursday");
                break;
            case 5:
                System.out.println("Friday");
                break;
            case 6:
                System.out.println("Saturday");
                break;
            default:
                System.out.println("发生错误");
        }
    }
}

JDK17之后增加了一个新特性：

import java.util.Scanner;

public class Test1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        a %= 7;
        int ans = 1;
        for(int i=1;i<=b;i++){
            ans *= a;
            ans %= 7;
        }
        switch(ans){
            case 0->{
                System.out.println("Sunday");
            }
            case 1-> {
                System.out.println("Monday");
            }
            case 2-> {
                System.out.println("Monday");
            }
            case 3-> {
                System.out.println("Wednesday");
            }
            case 4-> {
                System.out.println("Thursday");
            }
            case 5->{
                System.out.println("Friday");
            }
            case 6-> {
                System.out.println("Saturday");
            }
            default->{
                System.out.println("发生错误");
            }
        }
    }
}