P2-2 字符串的更多方法

字符串的更多方法

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String类主要成员1

String str1="你真是个大帅哥，yesyesyes";
//int length()字符串长度
System.out.println(str1.length());

//char charAt(int index) 获取第index个位置的字符
System.out.println(str1.charAt(5));

//boolean contains(CharSequence s)判断字符串s是否包含在本字符串中
System.out.println(str1.contains("y"));
System.out.println(str1.contains("Y"));

//String replace(CharSequence target,CharSequence replacement)
//把字符串中的target替换为replacement，字符串具有不可变性，因为旧的不变，要通过返回值拿新的
String str2 = str1.replace("大帅哥","cool");//在str1的字符串中选对对应的词来替换
System.out.println(str2);

String s ="I am likes job";
//String[]split(String regex)按照指定的字符串来拆分为多给字符串。参数是正则表达式类型，有特殊字符转义等问题，以后遇到再说
String[] strs =s.split(" ");//用空格来分割上面字符串
for (String str:strs)
{
    System.out.println(str);
}

//boolean startsWith("www") 判断字符串是否以WWW开头
//boolean endsWith("www") 判断字符串是否以WWW结尾
String str3 = "www.baidu.com";
System.out.println(str3.startsWith("www"));
System.out.println(str3.endsWith("www"));

String类主要成员2

String类主要成员3

练习

1、获取文件名

//自己写的
String s1= "c:/a/b/c.txt";
String s2= s1.substring(7);
System.out.println(s2);

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//获取/最后出现的下标，然后去截取字符串即可
String s1= "c:/a/b/c.txt";
int i1 = s1.lastIndexOf("/");
System.out.println(s1.substring(i1+1));

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2、获取后缀名

//自己写的
String s1= "c:/a/b/c.txt";
int i1= s1.lastIndexOf(".txt");
String s2=s1.substring(i1);
System.out.println(s2);

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//判断.最后出现的位置，然后从.的下标截取
String s1= "c:/a/b/c.txt";
int i1 = s1.lastIndexOf(".");
System.out.println(s1.substring(i1));

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3、判断

String userName ="admin";
String passWord="123456";
String userInputUserName = "ADMin";
String userInputpassWord="123456";
String newuserName = userName.trim();
if (newuserName.equalsIgnoreCase(userInputUserName))
{
    System.out.println("账号正确");
    if (passWord.equals(userInputpassWord))
    {
        System.out.println("密码正确");
    }
    else
    {
        System.out.println("密码错误");
    }
}
else
{
    System.out.println("账号错误");
}

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//简化后
String userInputUserName = "adMIN";
String userInputpassWord="123456";
if (userInputUserName.trim().equalsIgnoreCase("admin")&&userInputpassWord.equals("123456"))
{
    System.out.println(true);
}
else
{
    System.out.println(false);
}

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4、取前后的值

String s1="name=任cool";
String[] s2= s1.split("=");
System.out.println("这是等号前面的值："+s2[0]);
System.out.println("这是等号后面的值："+s2[1]);

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5、判断是否为jpg文件

//String s1= "c:/a/b/C.JPG";
String s1= "c:/a/b/C.TXT";
String s2=s1.toLowerCase(Locale.ROOT);
if (s2.contains(".jpg"))
{
    System.out.println("有jpg文件");
}
else
{
    System.out.println("没有jpg文件");
}

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//简化后
String s1= "c:/a/b/C.JPG";
System.out.println(s1.toLowerCase().contains(".jpg"));