[Java] 02 String的常用方法

public class TestString{
    public static void main(String[] args){
        String str1 = "123";
        String str2 = "456";
        String str3 = "678";
        StringBuilder sb1 = new StringBuilder();
        //StringBuilder支持链式编程；
        sb1.append(str1).append(str2);
        StringBuilder sb2 = sb1;
        sb2.append(str3);
        System.out.println(sb1.toString());//123456678
        
        //获取某个位置的字符，从0开始
        System.out.println(sb1.charAt(3));
        
        String str4 = "Hello";
        //大写转小写
        System.out.println(str4.toLowerCase());
        //小写转大写
        System.out.println(str4.toUpperCase());
        //字符串长度
        System.out.println(str4.length());//5
        
        String str5 = "hello world";
        //字符串替换
        System.out.println(str5.replace("world","you"));//hello you
        //替换原有字符串不会变
        System.out.println(str5);// hello world
        //是否以某个字符串开始
        System.out.println(str5.startsWith("hello"));//ture
        //是否以某个字符串结尾
        System.out.println(str5.endsWith("you"));//false
        
        //希望获取一个文件的后缀 -->dadggtad.txt
        String str6 = "t.txt";
        //截取字符串
        System.out.println(str6.substring(1,4));
        //获取某字符串的位置
        System.out.println(str6.indexOf("."));
        System.out.println(str6.substring(str6.lastIndexOf(".")+1));
        
        String word = "this is my world my name is Frost";
        String[] strs = word.split(" ");
        System.out.println(strs.length);
        for(String str:strs){
            System.out.println(str);
        }
        
        String str7 = "     dfajdfaj  ；dfja   ";
        //去除字符串前面和后面的空格
        System.out.println("|"+str7.trim()+"|");
    }
}