Java中String的常用方法

{
    //public char charAt(int index)
    //取出指定索引的字符
    String str = "hello";
    char c = str.charAt(1);
    System.out.println(c);
}

{
    //public char[] toCharArray()
    //字符数组与字符串的转换 
    String str = "hello";
    char[] strInCharArray = str.toCharArray();
    for(char item : strInCharArray)
    {
        System.out.print(item + " ");
    }
    System.out.println();
}

{
    //public char[] toCharArray()
    //判断一个给定的字符串是否有数字组成
    String str = "13212A355565";
    char[] strInCharArray = str.toCharArray();
    boolean flag = true;
    for(char item : strInCharArray)
    {
        if(item < ‘0‘ || item > ‘9‘)
        {
            flag = false;
            break;
        }
    }
    
    System.out.print(str + ": ");
    if(flag)
    {
        System.out.println("全部由数字组成!");
    }
    else
    {
        System.out.println("不是全由数字组成!");
    }
}

//public byte[] getBytes()
//字符串与字节数组的转换
String str = "hello world";
byte[] strInBytes = str.getBytes();
for(byte item : strInBytes)
{
    System.out.println((int)item);
}

String str1 = "hello";
String str2 = "HELLO";

System.out.println(str1.equals(str2));//false
System.out.println(str1.equalsIgnoreCase(str2));//true

String str = "hello world";
System.out.println(str.indexOf("world"));
System.out.println(str.indexOf("l"));
System.out.println(str.indexOf("l",5));
System.out.println(str.lastIndexOf("l"));