应风

深色模式

Strings ​

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Strings ​

java
String greeting = "Hello world!";
java
char[] helloArray = {'H', 'e', 'l', 'l', 'o'};
String helloString = new String(helloArray);
System.out.println(helloString.length());

长度 ​

java
String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
// 17

拼接 ​

java
String hello = "Hello";
String world = "World";

String helloWorld = hello + " " + world;

从 SE 15 开始，支持二维字符串文字：

java
String html = """
              <html>
                  <body>
                      <p>Hello, world</p>
                  </body>
              </html>
              """;
java
String fs;
fs = String.format("The value of the float " +
                   "variable is %f, while " +
                   "the value of the " +
                   "integer variable is %d, " +
                   " and the string is %s",
                   floatVar, intVar, stringVar);
System.out.println(fs);

数字 ​

字符串转换位数字 ​

java
public class ValueOfDemo {
    public static void main(String[] args) {

        // this program requires two
        // arguments on the command line
        if (args.length == 2) {
            // convert strings to numbers
            float a = (Float.valueOf(args[0])).floatValue();
            float b = (Float.valueOf(args[1])).floatValue();

            // do some arithmetic
            System.out.println("a + b = " +
                               (a + b));
            System.out.println("a - b = " +
                               (a - b));
            System.out.println("a * b = " +
                               (a * b));
            System.out.println("a / b = " +
                               (a / b));
            System.out.println("a % b = " +
                               (a % b));
        } else {
            System.out.println("This program " +
                "requires two command-line arguments.");
        }
    }
}
java
float a = Float.parseFloat(args[0]);
float b = Float.parseFloat(args[1]);

数字转换为字符串 ​

java
int i;
// Concatenate "i" with an empty string; conversion is handled for you.
String s1 = "" + i;

// The valueOf class method.
String s2 = String.valueOf(i);

每个 Number 的子类都有一个 toString() 方法。

java
int i;
double d;
String s3 = Integer.toString(i);
String s4 = Double.toString(d);

索引获取字符和子字符串 ​

java
String s = "Hello World";
char c = s.charAt(0);

char[] buf = new char[5];
s.getChars(0, 5, buf, 0);

搜索匹配 ​