分别用命令行参数，Scanner，JOptionPane和IO流实现对圆的面积和周长的求解

本文链接：https://blog.youkuaiyun.com/KLFTESPACE/article/details/88802784

本文通过四种不同的Java输入方式：命令行参数、Scanner类、JOptionPane对话框及BufferedReader字符流，展示了如何计算圆的面积和周长。

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//分别用命令行参数，Scanner，JOptionPane和IO流实现对圆的面积和周长的求解

BufferedReader字符流

System.in字节流

InputStreamReader字节流转字符流

BufferedReader的read（）是把第一个字符的ASCLL码赋值给变量

rreadLine()每次读回来的都是一行字符串

package firsthomework;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;

import javax.swing.JOptionPane;

public class Circle {

	public static void main(String[] args) throws IOException {

		
		//命令行参数		
		int r1 = Integer.parseInt(args[0]);
		
		System.out.println("圆的面积为"+Math.PI*r1*r1);
		System.out.println("圆的周长为"+Math.PI*2*r1);
		
		Scanner sc = new Scanner(System.in);
		
		System.out.println("输入圆的半径：");
		
		int r = sc.nextInt();
		
		System.out.println("圆的面积为"+Math.PI*r*r);
		System.out.println("圆的周长为"+Math.PI*2*r);
		
		String s = JOptionPane.showInputDialog(null,"请输入圆的半径：\n","圆",JOptionPane.PLAIN_MESSAGE);
		
		r = Integer.parseInt(s);
		JOptionPane.showMessageDialog(null,"圆的周长为:"+Math.PI*2*r, "圆", JOptionPane.INFORMATION_MESSAGE);
		JOptionPane.showMessageDialog(null,"圆的面积为:"+Math.PI*r*r, "圆", JOptionPane.INFORMATION_MESSAGE);
		
		System.out.println("输入圆的半径：");
		
		BufferedReader br = new BufferedReader(new InputStreamReader (System.in));
		String s1 = br.readLine();
		
		r = Integer.parseInt(s1);
		
		System.out.println("圆的面积为"+Math.PI*r*r);
		System.out.println("圆的周长为"+Math.PI*2*r);

	
	}

}