java学习笔记（2）

1.if条件语句

package daigua2;
/*
 * if条件语句有三种写法
 * */
public class IfElse1 {
    public static void main(String[] args) {
        int a = 10;
        int b = 10;
        // 写法1
        if(a==b) {
            System.out.println("a等于b!");
        }
        // 写法2
        a = 99;
        if (a % 2 == 0) {
            System.out.println("a是偶数！");
        } else {
            System.out.println("a是奇数！");
        }
        
        // 写法3
        if (a < 10) {
            System.out.println("a太小了！");
        } else if (a < 50){
            System.out.println("a还可以！");
        } else {
            System.out.println("a太大了！");
        }
        
    }
    
}

2.switch语句

package daigua2;
import java.util.Scanner;

public class Switch1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("请输入星期数:");
        
        int weekDay = sc.nextInt();
        
        switch (weekDay) {
        case 1:
            System.out.println("今天是星期1");
            break;
        case 2:
            System.out.println("今天是星期2");
            break;
        case 3:
            System.out.println("今天是星期3");
            break;
        case 4:
            System.out.println("今天是星期4");
            break;
        case 5:
            System.out.println("今天是星期5");
            break;
        case 6:
            System.out.println("今天是星期6");
            break;
        case 7:
            System.out.println("今天是星期7");
            break;
        default:
            System.out.println("输入错误！");
            break;
        }
        sc.close();
        
    }
}

3.for循环

package daigua2;
/*
 * for循环的使用
 * */
public class For1 {
    public static void main(String[] args) {
        int sum = 0;
        for(int i=1; i<10 ; i++) {
            System.out.println(i);
            sum += i;
        }
        System.out.println(sum);
    }
}

4.while循环

package daigua2;

public class While1 {
    public static void main(String[] args) {
        int sum = 0;
        int i = 1;
        
        while(i<=100) {
            sum += i++;
        }
        System.out.println(sum);
    }
}

5.do while循环

package daigua2;

public class DoWhile {
    public static void main(String[] args) {
        int sum = 0;
        int i = 1;
        
        do {
            sum += i++;
        } while (i <= 100);
        System.out.println(sum);
    }
}

6.循环控制break 和 continue

package daigua2;
/*
 * break 跳出当前循环
 * continue 跳出本次循环
 * */
public class Break_Continue {
    public static void main(String[] args) {
        
        for(int i=0; i<10; i++) {
            if(i==5) {
                break;
            }
            System.out.print(i + " ");
        }
        System.out.println();
        for(int i=0; i<10; i++) {
            if(i==5) {
                continue;
            }
            System.out.print(i + " ");
        }
    }
}