Java学习笔记--方法

Java方法

创建加法

public class Demo01 {
   public static void main(String[] args) {
       int a = 0;
       a = add(1,2);
       System.out.println(a);
   }
   public static int add(int x, int y){
       return  x  + y;
   }
}

方法结构

public class Demo02 {
    public static void main(String[] args) {
        System.out.println(max(2,4));
    }
    public static int max(int x, int y){
        if(x==y)
            return 0;//终止方法
        if(x>y)
            return x;
        else
            return y;
    }
}

方法重载

public class Demo02 {
    public static void main(String[] args) {
        System.out.println(max(2,4));
    }
    public static int max(int x, int y){
        if(x==y)
            return 0;//终止方法
        if(x>y)
            return x;
        else
            return y;
    }
    public static double max(double x, double y){ //方法重载，参数类型不同
        if(x==y)
            return 0;
        if(x>y)
            return x;
        else
            return y;
    }
}

命令行传参

public class Demo03 {
    public static void main(String[] args) {
        for (int i = 0; i < args.length; i++) {
            System.out.println("args["+i+"]:" +args[i]);
        }
    }
}

命令：

CodeSource> javac Demo03.java #文件路径
ProjectSorce\src> L1_packege.L2_packege.Demo03 Parameter #包路径加参数

可变参数

public class Demo04 {
    public static void main(String[] args) {
        int[] i = { 1,2,3,4,5};
        test(i);
    }
    public static void test(int...i){ //本质上是一个数组
        for(int x:i){
            System.out.print(x+"\t");
        }
    }
}

//输入5个数字比大小
public class Demo05 { 
    public static void main(String[] args) {
        double[] numbers = {1,2,3,4,5};
        int i = 0;
        Scanner scanner = new Scanner(System.in);
        for (int i1 = 0; i1 < 5; i1++) {
            numbers[i] = scanner.nextDouble();
            i++;
        }
        printMax(numbers);
    }
    public static double printMax(double... numbers){
        if(numbers.length==0){
            System.out.println("No Number");
            return 0;
        }
        double result = numbers[0];
        for (int i = 1; i < numbers.length; i++) {
            if (numbers[i] > result )
                result = numbers[i];
        }
        System.out.println("The max value is" + result);
        return 0;
    }
}

递归

public class Demo06 { // 输入一个数字阶乘
    public static void main(String[] args) {
        System.out.println("输入数字: ");
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        System.out.println(n+"的阶乘为"+test(n));
    }
    public static long test(int n){
         if((n==1)||(n==0))
             return 1;
         else
             return n*test(n-1);
    }
}

简单的计算器实现

public class SimpleCalculator {
    public static void main(String[] args) {
        System.out.println("计算器输入格式 x 运算符 y,请输入");
        Scanner scanner = new Scanner(System.in);
        double x = scanner.nextDouble();
        String sym = scanner.next();
        double y = scanner.nextDouble();
        System.out.println("结果等于"+cal(x,sym,y));
        }
    public static double cal(double x,String sym,double y){
        double result = 0;
        switch (sym){
            case "*":
                result = x*y;break;
            case "/":
                result = x/y;break;
            case "+":
                result = x+y;break;
            case "-":
                result = x-y;break;
            default:
                System.out.println("输入错误!");
                return 0;
        }
        return result;
    }
}