Java字符串字符
字符所在的索引
可以使用charAt()
方法從String
對象中獲取指定索引處的字符。索引值是從零開始的。以下代碼在「YIIBAI.COM
」字符串中打印索引值和每個索引處對應的字符:
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);
}
}
}
上面的代碼生成以下結果。
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
測試字符串是否爲空
測試String
對象是否爲空,空字符串的長度爲零。有三種方法可以檢查空字符串:
- isEmpty() 方法.
- equals() 方法.
- 獲取字符串的長度,並檢查它是否爲零。
以下代碼顯示如何使用三種方法:
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
}
}
更改字符的大小寫
要將字符串的內容轉換爲小寫和大寫,請分別使用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"