Java方法

System.out.printIn()

类.方法.对象

public static void main()

public 修饰符

static 类变量

void 返回值类型 void代表不返回东西

main 方法名

package com.xiaojie.method;

public class Demo01 {
    public static void main(String[] args) {
        int sum = add(1, 2);
        System.out.println(sum);

        System.out.println("=============================");
        test();
    }

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

    public static void test(){
        int i = 0;
        while (i<=1000) {
            i++;
            if (i%5==0) {
                System.out.print(i+"	");
            }
            if (i%(5*3)==0) {
                System.out.print("
");
            }
        }
    }
}

package com.xiaojie.method;

public class Demo01 {
    public static void main(String[] args) {

        //实际参数：实际调用传递给他的参数
        int sum = add(1, 2);
        System.out.println(sum);
    }

    //加法
    //形式参数，用来定义作用的
    public static int add(int a,int b) {
        return a+b;
    }
}

package com.xiaojie.method;

public class Demo02 {
    public static void main(String[] args) {
        int max = max(10,10);
        System.out.println(max);
    }

    //比大小
    public static int max(int num1,int num2) {

        int result = 0;
        if (num1==num2) {
            System.out.println("两次输入的数值相等");
            return 0; //终止方法，类似while中的break
        }else if (num1 > num2) {
            result = num1;
        }else {
            result = num2;
        }

        return result;
    }
}

package com.xiaojie.method;

public class Demo02 {
    public static void main(String[] args) {
        int max = max(20,10,30);
        System.out.println(max);
    }

    //比大小
    public static int max(int num1,int num2) {

        int result = 0;
        if (num1==num2) {
            System.out.println("两次输入的数值相等");
            return 0; //终止方法，类似while中的break
        }else if (num1 > num2) {
            result = num1;
        }else {
            result = num2;
        }

        return result;
    }
    //比大小
    public static double max(double num1,double num2) {

        double result = 0;
        if (num1==num2) {
            System.out.println("两次输入的数值相等");
            return 0; //终止方法，类似while中的break
        }else if (num1 > num2) {
            result = num1;
        }else {
            result = num2;
        }

        return result;
    }
    //比大小
    public static int max(int num1,int num2,int num3) {

        int result = 0;
        if (num1==num2) {
            System.out.println("两次输入的数值相等");
            return 0; //终止方法，类似while中的break
        }else if (num1 > num2) {
            result = num1;
        }else {
            result = num2;
        }

        return num3;
    }
}

package com.xiaojie.method;

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

D:JavaSE基础语法srccomxiaojiemethod>javac Demo03.java

D:JavaSE基础语法srccomxiaojiemethod>java Demo03
错误: 找不到或无法加载主类 Demo03

D:JavaSE基础语法srccomxiaojiemethod>cd ../../../

D:JavaSE基础语法src>java com.xiaojie.method.Demo03

D:JavaSE基础语法src>java com.xiaojie.method.Demo03 Hello World !
args[0]: Hello
args[1]: World
args[2]: !

package com.xiaojie.method;

public class Demo04 {
    public static void main(String[] args) {
        Demo04 demo04 = new Demo04();
        demo04.printMax(10,40,20,50,100,23);
        demo04.printMax(new double[] {1,2,4,5,3});
    }
    public void printMax (double... numbers) {
        if (numbers.length == 0) {
            System.out.println("输入有误请重试");
            return;
        }
        double result = numbers[0];
        for (int x = 1; x < numbers.length; x++) {
            if (numbers[x] > result) {
                result  = numbers[x];
            }
        }
        System.out.println(result);
    }
}

边界条件：边界

前阶段：当参数不等于1时，不停调用自身直到等于1的时候，返回了结果

放回阶段：从最大的数开始 n*(n-1)

Java属于栈机制

package com.xiaojie.method;

public class Demo05 {
    //阶乘
    //2!    2*1
    //3!    3*2*1
    //4!    4*3*2*1
    public static void main(String[] args) {
        System.out.println(f(5));
    }

    public static int f(int n){
        if (n == 1) {
            return 1;
        }else {
            return n*f(n-1);
        }
    }

}

字符交互简易计算器

package com.xiaojie.method;

import java.util.Scanner;

public class Demo07 {
    /*
计算机
接收用户的数据，写四个方法负责加减乘除
利用循环和switch进行交互
 */
    public static void main(String[] args) {
        System.out.println("输入要计算的格式");
        Scanner scanner = new Scanner(System.in);
        String s = scanner.next();
        switch (s){
            case "+" :
                Demo07 add = new Demo07();
                add.addition();
                break;
            case "-" :
                Demo07 sub = new Demo07();
                sub.subtraction();
                break;
            case "*" :
                Demo07 mul = new Demo07();
                mul.multiply();
                break;
            case "/" :
                Demo07 div = new Demo07();
                div.division();
                break;
            default :
                System.out.println("请选择 + - * / ");
        }


    }
    public double addition() {
        double num = 0;
        int x = 0;
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入数字");
        while (scanner.hasNextDouble()) {
            double i = scanner.nextDouble();
            num += i;
            x++;
            System.out.println("当前输入第"+x+"次，本次输入的数字是"+i);
        }
        System.out.println("合计："+num);
        scanner.close();
        return 0;
    }
    public double subtraction() {
        double num = 0;
        int x = 0;
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入数字");
        while (scanner.hasNextDouble()) {
            double i = scanner.nextDouble();
            num -= i;
            x++;
            System.out.println("当前输入第"+x+"次，本次输入的数字是"+i);
        }
        System.out.println("合计："+num);
        scanner.close();
        return 0;
    }
    public double multiply() {
        double num = 1;
        int x = 0;
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入数字");
        while (scanner.hasNextDouble()) {
            double i = scanner.nextDouble();
            num *= i;
            x++;
            System.out.println("当前输入第"+x+"次，本次输入的数字是"+i);
        }
        System.out.println("合计："+num);
        scanner.close();
        return 0;
    }
    public double division() {
        double num = 0.0;
        int x = 0;
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入数字");
        while (scanner.hasNextDouble()) {
            double i = scanner.nextDouble();
            if (num == 0.0) {
                num = i;
                x++;
                System.out.println("当前输入第"+x+"次，本次输入的数字是"+i);
                continue;
            }
            num /= i;
            x++;
            System.out.println("当前输入第"+x+"次，本次输入的数字是"+i);
        }
        System.out.println("合计："+num);
        scanner.close();
        return 0;
    }
}