What are the commonly used string tools in Java function libraries?

The Java language provides a series of string processing function libraries, including: string concatenation, string comparison, string formatting, string search and string replacement. These tools can simplify the processing of string data and improve development efficiency. This article describes how to use these tools and provides a code example that uses the string tools to read and process a CSV file.

Commonly used string tools in the Java function library

The Java language provides a rich string processing function library, which can Helps developers handle string data easily. This article will introduce some of the most commonly used string tools and provide a practical case to illustrate the use of these tools.

1. String concatenation

• Operator: Concatenate two strings.
• StringBuilder Class: Concatenate multiple strings more efficiently.
• String.join(String, String[]): Join the string array into a string.

String str1 = "Hello";
String str2 = "World";
String concatenated = str1 + " " + str2; // 使用 + 操作符
StringBuilder sb = new StringBuilder();
sb.append(str1).append(" ").append(str2); // 使用 StringBuilder
String joined = String.join(" ", str1, str2); // 使用 String.join

2. String comparison

• == and !=: compare characters Whether the string values ​​are equal.
• String.equals(String): Compare string values ​​for equality (case sensitive).
• String.equalsIgnoreCase(String): Compares string values ​​for equality (not case-sensitive).

String str1 = "java";
String str2 = "Java";
boolean equal = str1 == str2; // 比较值，结果为 false
boolean equals = str1.equals(str2); // 比较值，结果为 false
boolean equalsIgnoreCase = str1.equalsIgnoreCase(str2); // 比较值，结果为 true

3. String formatting

• String.format(String, Object...): Use Placeholder format string.
• printf(String, Object...): Format console output.

String name = "John Doe";
int age = 25;
String formatted = String.format("Name: %s, Age: %d", name, age);
System.out.printf("Name: %s, Age: %d", name, age);

4. String search

• String.indexOf(String): Find the specified substring in the character The index of the first occurrence in the string.
• String.lastIndexOf(String): Find the index of the last occurrence of the specified substring in the string.
• String.contains(String): Check whether the string contains the specified substring.

String str = "This is a test string";
int firstIndex = str.indexOf("is"); // 查找首次出现的 "is"
int lastIndex = str.lastIndexOf("is"); // 查找最后一次出现的 "is"
boolean contains = str.contains("test"); // 检查是否包含 "test"

5. String replacement

• String.replace(String, String): Replace a substring Replaced with another substring.
• String.replaceAll(String, String): Replace all matching substrings with another substring.

String str = "The quick brown fox";
String replaced = str.replace("quick", "slow"); // 替换 "quick" 为 "slow"
String replacedAll = str.replaceAll("[aeiou]", "*"); // 将所有元音替换为 "*"

Practical case: Reading and processing CSV files

The following code shows how to use string tools to read and process CSV files:

import java.io.BufferedReader;
import java.io.FileReader;

public class CSVReader {

    public static void main(String[] args) {
        try (BufferedReader reader = new BufferedReader(new FileReader("data.csv"))) {
            String line;
            while ((line = reader.readLine()) != null) {
                String[] data = line.split(","); // 使用 split() 分割 CSV 行
                for (String item : data) {
                    // 对每项数据进行处理
                    System.out.println(item.trim()); // 使用 trim() 去除空格
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

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