Java -day2

三 流程控制

3.1 scanner

psvm 

new Scanner(System.in)  alt+enter+enter  自动补全

 

Scanner scanner = new Scanner(System.in);

System.out.println("使用next方法接受：");

if(scanner.hasNext()){
    String str = scanner.next();
    System.out.println(str);

    System.out.println(scanner.nextInt());
　　 System.out.println(scanner.nextFloat());

}

Scanner.close();  //及时关闭

3.2 if

public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        String s = scanner.nextLine();
        if(s.equals("hello")){
            System.out.println(s);
        }else {
            System.out.println("not hello");
        }
        System.out.println("end");
        scanner.close();
    }

3.3 switch

public static void main(String[] args) {
        char grade = 'C';

        switch (grade){
            case 'A':
                System.out.println("优秀");
                break;//可选  case穿透 没看见break就继续执行
                //不屑break就会在条件之后顺着执行
            case 'B':
                System.out.println("优秀-");
                break;
            case 'C':
                System.out.println("优秀--");
                break;
            case 'D':
                System.out.println("优秀---");
                break;
            default:
                System.out.println("未知");

        }
    }

public static void main(String[] args) {
        String name = "fxh";

        switch (name){
            case "fxh":
                System.out.println("fxh");
                break;
            case "xxx":
                System.out.println("xxx");
                break;
            default:
                System.out.println("??");
        }
    }

3.4 while

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

3.5 for

public static void main(String[] args) {
        int sum1 = 0;
        int sum2 = 0;
        for (int i = 1; i<=100;i++) {
            if (i%2 == 0)
                sum2+=i;
            else sum1+=i;
        }

        System.out.println("奇数和" + sum1);//oddSum
        System.out.println("偶数和" + sum2);//evenSum

println 输出自动换行  print 不换行

public static void main(String[] args) {
        int count = 0;
        for (int i = 0;i<1000;i++){
            if (i%5 == 0){
                System.out.print( i +"\t");
            }
            if (i%15 ==0){
                System.out.println();
            }
        }
    }

public class ForDemo03 {
    public static void main(String[] args) {
        //九九乘法表
        for (int i = 1;i < 10 ; i++){
            for (int j = 1;j <= i;j++){
                System.out.print( j + "*" + i + "=" + i*j +"\t");
            }
            System.out.println();
        }
    }
}

10.for  自动生成

for (int i = 0; i < 10; i++) {
            
        }

3.6 加强for

public static void main(String[] args) {
        int[] number = {10,20,30,40,50};
        for (int x:number){
            System.out.println(x);
        }
    }

3.7 break、continue、goto

break 跳出循环 不终止程序

cintitune 跳出此次循环 不终止循环

goto 

3.8 打印三角形 debug

拆成两部分 先打空白 再打星

 public static void main(String[] args) {
        //五行的三角形
        for (int i = 0; i < 5; i++) {
            for (int j = 5; j >= i; j--){
                System.out.print(" ");
            }
            for (int j = 0; j <= i; j++){
                System.out.print("*");
            }
            for (int j = 1; j <= i; j++){
                System.out.print("*");
            }
            System.out.println();
        }
                   
    }

 

 四 方法

 4.1 什么是方法

 

public class Demo01 {
    public static void main(String[] args) {
        int add = add(1,3);
        System.out.println(add);

    }
    public static int add(int a,int b){  //static 类变量
        return a+b;
    }


}

 

4.2 方法定义

命名 开头小写 驼峰大写

调用

//比大小
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNextInt()){
            int a = scanner.nextInt();
            int b = scanner.nextInt();
            System.out.println(max(a,b));
        }
    }

    public static int max(int a,int b){
        int resout = 0;
        if (a>b){
            resout = a;
        }else if (b>a){
            resout = b;
        }else {
            System.out.println("a==b");
            return 0; //终止方法
        }
        return resout;
    }

 

 4.3 方法重载

 方法名字可以相同 参数类型不同、个数不同

 

 

Java方法04：命令行传递参数_哔哩哔哩_bilibili  P48