java字符大小写转换——toLowerCase方法

╰+哭是因爲堅強的太久メ 2024-03-22 14:19 77阅读 0赞

1.手动实现

public class Test {
        
        public static String my_toLowerCase(String str) {
        
            String ret = "";
            for (int i = 0; i < str.length(); i++) {
        
                char ch = str.charAt(i);
                if (ch >= 'A' && ch <= 'Z') {
        
                    ch = (char) (ch + 32);
                    ret = ret + ch;
                } else {
        
                    ret = ret + ch;
                }
            }
            return ret;
        }
    
        public static void main(String[] args) {
        
            String str = "hello 123 BAIXIAN";
            String ret = my_toLowerCase(str);
            System.out.println(ret);
    
        }
    }

![在这里插入图片描述][7b4686919fbe4c9f84e23e16f1e99f7e.png]

此外，实际上在实现`my_toLowerCase`过程中new了很多对象，这是效率非常低的，可以采用SringBuilderl类型，这样本身去调用append方法就效率高一些

public class Test {
        
    
        public static String my_toLowerCase(String str) {
        
            StringBuilder stringBuilder = new StringBuilder();
            for (int i = 0; i < str.length(); i++) {
        
                char ch = str.charAt(i);
                if (ch >= 'A' && ch <= 'Z') {
        
                    ch = (char) (ch + 32);
                    stringBuilder.append(ch);
                } else {
        
                    stringBuilder.append(ch);
                }
            }
            return stringBuilder.toString();
        }
    
        public static void main(String[] args) {
        
            String str = "hello 123 BAIXIAN";
            String ret = my_toLowerCase(str);
            System.out.println(ret);
    
        }
    }

2.利用Java中String的原生方法

public class Test {
        
        public static void main(String[] args) {
        
            String str1 = "HELLO,你好";
            String str2 = "hello,你好";
            String str3 = "HEllo";
            System.out.println(str2.toLowerCase());//转换成小写
            System.out.println(str2.toUpperCase());//转换成大写
            System.out.println(str3.toLowerCase());
        }
    }

[7b4686919fbe4c9f84e23e16f1e99f7e.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/22/705a2266b9974e81be8a6ed90d268e46.png