java学习之string类的字符串大小写之间的转换

package com.ifenx8.study.test;

import javax.print.DocFlavor.STRING;

public class Demo1_Test1 {
	public static void main(String[] args) {
		//dome1();
		//demo2();
		//吧数组中的数据按照指定的格式拼接成一个字符串
		//int[] arr = {1 ,2 ,3}; 结果为： "[1, 2, 3]"
		int [] arr = {1, 2, 3};
		String s1 = String.valueOf(arr);
		String s2 = "[";
		for (int i = 0; i < arr.length; i++) {
		
			
	if (i ==2){
		s2 = s2 + arr[i] + "]";
	}else{
		s2 = s2 + arr[i] + ", ";
		}
		
		}
		System.out.print(s2);
	}

	public static void demo2() {
		//要求字符串首字母大写其余的字符都小写
		String s1 = "woaIzhOngGuO";
		String s2 = s1.substring(0, 1).toUpperCase().concat(s1.substring(1).toLowerCase());
		System.out.println(s2);
	}

	public static void dome1() {
		
		String s1= "aFGFdgdfdgTGRHGSgdfgedgGga";
		String s2 = s1.toLowerCase();//把字符串全部转换成小写字母
		System.out.println(s2);
		String s3 = s1.toUpperCase();//把字符串全部转换成大写字母
		System.out.println(s3);
		String s4 = s2.concat(s3);//吧两个字符串拼接起来
		System.out.println(s4);
	}
}