Java字符串字符

傷城~ 2022-09-30 12:48 119阅读 0赞

## 字符所在的索引 ##

可以使用`charAt()`方法从`String`对象中获取指定索引处的字符。索引值是从零开始的。以下代码在“`YIIBAI.COM`”字符串中打印索引值和每个索引处对应的字符：

public class Main { public static void main(String[] args) { String str = "YIIBAI.COM"; // Get the length of string YIIBAI.COM int len = str.length(); // Loop through all characters and print their indexes for (int i = 0; i < len; i++) { System.out.println(str.charAt(i) + " has index " + i); } } } 
      
       Java

上面的代码生成以下结果。

Y has index 0 I has index 1 I has index 2 B has index 3 A has index 4 I has index 5 . has index 6 C has index 7 O has index 8 M has index 9 
      
       Java

## 测试字符串是否为空 ##

测试`String`对象是否为空，空字符串的长度为零。有三种方法可以检查空字符串：

*  isEmpty() 方法.
 *  equals() 方法.
 *  获取字符串的长度，并检查它是否为零。

以下代码显示如何使用三种方法：

public class Main { public static void main(String[] args) { String str1 = "Hello"; String str2 = ""; // Using the isEmpty() method boolean empty1 = str1.isEmpty(); // Assigns false to empty1 boolean empty2 = str2.isEmpty(); // Assigns true to empty1 // Using the equals() method boolean empty3 = "".equals(str1); // Assigns false to empty3 boolean empty4 = "".equals(str2); // Assigns true to empty4 // Comparing length of the string with 0 boolean empty5 = str1.length() == 0; // Assigns false to empty5 boolean empty6 = str2.length() == 0; // Assigns true to empty6 } } 
      
       Java

## 更改字符的大小写 ##

要将字符串的内容转换为小写和大写，请分别使用`toLowerCase()`和`toUpperCase()`方法。

String str1 = new String("Hello"); // str1 contains "Hello" String str2 = str1.toUpperCase(); // str2 contains "HELLO" String str3 = str1.toLowerCase(); // str3 contains "hello"