String函数以及控制台输入输出(Java)

本程序使用了Java中一些String函数对字符串进行了操作，展示了其用法。同时展示了Java的控制台输入输出的方法。程序代码如下：

package com.string.demo;
import static java.lang.Math.*;//sqrt()函数需要声明此头文件
import java.util.*;
public class MyFirstJava {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		//math
		System.out.println("the square root of \u03c0 is "+ sqrt(PI));
		//string 声明
		String s = "Hello";
		//子串获得；begin from 0,size is 3
		String sub = s.substring(0,3);
		//拼接
		String s_sub = s+"Hel";
		System.out.println("子串为"+sub);
		System.out.println("拼接string和子串为"+s_sub);
		sub = sub + "lo";
		//检查两个字符串是否相等，str1.equals(str2);
		//don't use "==" to check
		System.out.println("检查两个string是否相等的结果为"+s_sub.equals(sub));
		//检查两个字符串是否相等，忽略大小写
		System.out.println("检查两个string是否相等的结果为"+sub.equalsIgnoreCase("hel"));
		/*
		 * 检查空串
		 * str.length == 0;或者str.equals("");
		 * null串
		 * 如果在构造器中没有显式地给域赋初值，就会自动被赋予默认值
		 * 数值初始值为0；bool值为false；对象引用为null；
		 * */
		//字符串小写变大写
		System.out.println("字符串全部转换为小写："+sub.toLowerCase());
		//字符串大写变小写
		System.out.println("字符串全部转换为大写："+sub.toUpperCase());
		//取代
		System.out.println("用abcde取代el："+sub.replace("el", "abcde"));
		//sub won't change,return a new string
		sub = " "+sub+" ";
		System.out.println(sub);
		System.out.println("去掉sub的空格结果为："+sub.trim());//remove " " in head and tail
		//input and output in java
		//通过控制台输入首先需要构造一个Scanner对象，并与“标准输入流”System.in关联
		Scanner in = new Scanner(System.in);
		//然后使用Scanner类的各种方法实现输入操作
		System.out.println("What's your name?");
		String name = in.nextLine();//可以输入一行内容，包括空格
		System.out.println("your name is "+name);
		//读取一个单词，空格作为分隔符
		System.out.println("What's your first name?");
		String firstname = in.next();
		System.out.println("your first name is "+firstname);
		//读取一个整数
		System.out.println("What's your age?");
		int age = in.nextInt();
		System.out.println("your age is "+age);
		//读取一个浮点数
		System.out.println("What's your grade?");
		double grade = in.nextInt();
		System.out.println("your grade is "+grade);
	}

}

运行结果如下：

the square root of π is 1.7724538509055159
子串为Hel
拼接string和子串为HelloHel
检查两个string是否相等的结果为false
检查两个string是否相等的结果为false
字符串全部转换为小写：hello
字符串全部转换为大写：HELLO
用abcde取代el：Habcdelo
 Hello 
去掉sub的空格结果为：Hello
What's your name?
Li Ming
your name is Li Ming
What's your first name?
Ming
your first name is Ming
What's your age?
16
your age is 16
What's your grade?
120
your grade is 120.0

全文完

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