一篇文章看懂Java字符串操作

目錄

• ✨字符, 字節與字符串
• 🎈字符與字符串
• 🎈字節與字符串
• ✨字符串常見操作
• 🎈字符串比較
• 🎈字符串查找
•  🎈字符串替換
•  🎈字符串拆分
•  🎈字符串截取
• 🎈其他操作方法
• 總結

 public static void main(String[] args) {
        String str = "hello" ;
        System.out.println(str.charAt(0));// 下標從 0 開始
        System.out.println(str.charAt(1));
        System.out.println(str.charAt(2));
        System.out.println(str.charAt(3));
 
    }

 public static void main(String[] args) {
        String str = "helloworld" ;
        // 將字符串變為字符數組
        char[] data = str.toCharArray() ;
        for (int i = 0; i < data.length; i++) {
            System.out.print(data[i]+" ");
        }
 
    }

public static void main(String[] args) {
        String str = "helloworld" ;
        // 將字符串變為字符數組
        char[] data = str.toCharArray() ;
        // 字符數組轉為字符串
        System.out.println(new String(data)); // 全部轉換
        System.out.println(new String(data,5,5)); // 部分轉換
    }

public static boolean isNumberChar(String s) {
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            //判斷某個字符是不是數字
            if(c < '0' || c > '9') {
                return false;
            }
 
        }
        return true;
    }

 public static void main(String[] args) {
        String str = "124567";
        System.out.println(isNumberChar(str));
    }

public static void main(String[] args) {
        String str = "1d4567";
        System.out.println(isNumberChar(str));
    }

public static void main(String[] args) {
        String str = "helloworld" ;
        // String 轉 byte[]
        byte[] data = str.getBytes() ;
        for (int i = 0; i < data.length; i++) {
            System.out.print(data[i]+" ");
        }
        System.out.println();
        // byte[] 轉 String
        System.out.println(new String(data));
    }

 public static void main(String[] args)  {
        byte[] bytes = {97,98,99,100};
        String str = new String(bytes,1,3);
        System.out.println(str);
 
    }

 public static void main(String[] args) {
        String str1 = "hello" ;
        String str2 = "Hello" ;
        System.out.println(str1.equals(str2)); // false
        System.out.println(str1.equalsIgnoreCase(str2)); // true 
    }

 public static void main(String[] args) {
        System.out.println("A".compareTo("a")); // -32
        System.out.println("a".compareTo("A")); // 32
        System.out.println("A".compareTo("A")); // 0
        System.out.println("AB".compareTo("AC")); // -1
        System.out.println("劉".compareTo("楊"));
    }

public static void main(String[] args) {
        String str = "helloworld" ;
        System.out.println(str.contains("world")); 
        System.out.println(str.contains("forld"));
    }

public static void main(String[] args) {
        String str = "helloworld" ;
        System.out.println(str.indexOf("world")); // 5,w開始的索引
        System.out.println(str.indexOf("bit")); // -1，沒有查到
        if (str.indexOf("hello") != -1) {
            System.out.println("可以查到指定字符串！");
        }
    }

 public static void main(String[] args) {
        String str = "helloworld" ;
        System.out.println(str.indexOf("l")); // 2
        System.out.println(str.indexOf("l",5)); // 8
        System.out.println(str.lastIndexOf("l")); // 8
    }

public static void main(String[] args) {
        String str = "**@@helloworld!!" ;
        System.out.println(str.startsWith("**")); // true
        System.out.println(str.startsWith("@@",2)); // ture
        System.out.println(str.endsWith("!!")); // true
    }

 public static void main(String[] args) {
        String str = "helloworld" ;
        System.out.println(str.replaceAll("l", "_"));
        System.out.println(str.replaceFirst("l", "_"));
    }

  public static void main(String[] args) {
        String str = "hello world hello yu" ;
        String[] result = str.split(" ") ; // 按照空格拆分
        for(String s: result) {
            System.out.println(s);
        }
    }

public static void main(String[] args) {
        String str = "hello world hello yu" ;
        String[] result = str.split(" ",2) ;
        for(String s: result) {
            System.out.println(s);
        }
    }

public static void main(String[] args) {
        String str = "192.168.1.1" ;
        String[] result = str.split("\\.") ;
        for(String s: result) {
            System.out.println(s);
        }
    }

public static void main(String[] args) {
        String str = "name=zhangsan&age=18" ;
        String[] result = str.split("&") ;
        for (int i = 0; i < result.length; i++) {
            String[] temp = result[i].split("=") ;
            System.out.println(temp[0]+" = "+temp[1]);
        }
    }

public static void main(String[] args) {
        String str = "helloworld" ;
        System.out.println(str.substring(5));
        System.out.println(str.substring(0, 5));
    }