Java优学网String方法讲解：从基础操作到高效编程技巧，轻松掌握字符串处理

String str = "hello"; str = str + " world";

String text = "Hello世界"; System.out.println(text.length()); // 输出7

public boolean isValidEmail(String email) {

if (email == null || email.trim().isEmpty()) {
    return false;
}
String trimmedEmail = email.trim().toLowerCase();
return trimmedEmail.contains("@") && 
       trimmedEmail.indexOf("@") < trimmedEmail.lastIndexOf(".");

}

// 反例：每次循环都创建新String对象 public String buildStringBad(int n) {

String result = "";
for (int i = 0; i < n; i++) {
    result += "item" + i; // 每次循环都new StringBuilder，然后toString
}
return result;

}

// 正例：使用StringBuilder public String buildStringGood(int n) {

StringBuilder sb = new StringBuilder();
for (int i = 0; i < n; i++) {
    sb.append("item").append(i);
}
return sb.toString();

}

// 检查字符串是否匹配模式 String email = "user@example.com"; boolean isValid = email.matches("^[\w.-]+@[\w.-]+\.[a-z]{2,}$");

// 分割字符串 String csv = "Java,Python,Go,JavaScript"; String[] languages = csv.split(",\s*"); // 处理可能存在的空格

// 替换匹配内容 String text = "价格：$100, $200, $300"; String cleaned = text.replaceAll("\$", "￥"); // 替换所有美元符号