Java—switch case实现两个数的算术运算

方法一：

package com.liaojianya.chapter1;

import java.util.Scanner;

public class SwitchDemo1
{
	public static void main(String[] args)
	{
		Scanner input = new Scanner(System.in);
		System.out.println("Enter number a : ");
		double a = input.nextDouble();
		System.out.println("Enter number b : ");
		double b = input.nextDouble();
		Action ac = new Action(a, b);
		ac.command(Action.ADD);
		ac.command(Action.SUBTRACT);
		ac.command(Action.MULTIPLY);
		ac.command(Action.DIVIDE);
		ac.command(Action.MOD);
		input.close();
	}
}

class Action
{
	double a;
	double b;
	public Action(double a, double b)
	{
		this.a = a;
		this.b = b;
	}
	public static final int ADD = 1;
	public static final int SUBTRACT = 2;
	public static final int MULTIPLY = 3;
	public static final int DIVIDE = 4;
	public static final int MOD = 5;

	public void command(int c)
	{
		switch (c)
		{
		case 1:
			System.out.println(a + " + " + b + " = " + (a + b));
			break;

		case 2:
			System.out.println(a + " - " + b + " = " + (a - b));
			break;

		case 3:
			System.out.println(a + " * " + b + " = " + (a * b));
			break;

		case 4:
			System.out.println(a + " / " + b + " = " + (a / b));
			break;

		case 5:
			System.out.println(a + " % " + b + " = " + (a % b));
			break;

		default:
			System.out.println("unknown operation!");
			break;
		}
	}

}

　　方法二：

package com.liaojianya.chapter1;

import java.util.Scanner;

/**
 * This program demonstrates the use of switch.
 * @author LIAO JIANYA
 *
 */
public class SwitchDemo
{
	public static void main(String[] args)
	{
		Scanner input = new Scanner(System.in);
		
		System.out.println("Enter number a : ");
		double a = input.nextDouble();
		System.out.println("Enter number b : ");
		double b = input.nextDouble();
		System.out.println("Enter  operater :1代表+，2代表-，3代表*，4代表/，5代表% ");
		int c = input.nextInt();
		switch(c)
		{
			case 1:
			System.out.println(a + " + " + b + " = " + (a + b));
			break;

			case 2:
			System.out.println(a + " - " + b + " = " + (a - b));
			break;

			case 3:
			System.out.println(a + " * " + b + " = " + (a * b));
			break;

			case 4:
			System.out.println(a + " / " + b + " = " + (a / b));
			break;

			case 5:
			System.out.println(a + " % " + b + " = " + (a % b));
			break;
			
			default:
				System.out.println("unknown operation!");
				break;
		}
	}

}

　　运行结果：

Enter number a : 
12.3
Enter number b : 
32.1
12.3 + 32.1 = 44.400000000000006
12.3 - 32.1 = -19.8
12.3 * 32.1 = 394.83000000000004
12.3 / 32.1 = 0.38317757009345793
12.3 % 32.1 = 12.3