Characters in Java

Example 1: Use char when saving a character

package character;
 
public class TestChar {
 
    public static void main(String[] args) {
        char c1 = 'a';
        char c2 = '1';//Character 1, not number 1
        char c3 = 'in';//Chinese character
        char c4 = 'ab'; //Only one character can be placed.
         
    }
}

Example 2: Encapsulation class corresponding to char

Character corresponds to the encapsulation class

package character;
 
public class TestChar {
 
    public static void main(String[] args) {
        char c1 = 'a';
        Character c = c1; //Automatic boxing
        c1 = c;//Automatic dismantling
         
    }
}

Example 3: Common Character methods

package character;
 
public class TestChar {
 
    public static void main(String[] args) {
         
        System.out.println(Character.isLetter('a'));//Judge whether it's a letter or not
        System.out.println(Character.isDigit('a')); //Judging whether it is a number
        System.out.println(Character.isWhitespace(' ')); //Is it blank?
        System.out.println(Character.isUpperCase('a')); //Is it capitalized?
        System.out.println(Character.isLowerCase('a')); //Is it lowercase?
         
        System.out.println(Character.toUpperCase('a')); //Convert to uppercase
        System.out.println(Character.toLowerCase('A')); //Convert to lowercase
 
        String a = 'a'; //Can't convert a character directly into a string
        String a2 = Character.toString('a'); //Convert to String
         
    }
}

Example 4: Common escape

package character;
  
public class TestChar {
  
    public static void main(String[] args) {
        System.out.println("Alignment cannot be achieved by using spaces");
        System.out.println("abc def");
        System.out.println("ab def");
        System.out.println("a def");
          
        System.out.println("Use\\t Tables can achieve alignment");
        System.out.println("abc\tdef");
        System.out.println("ab\tdef");
        System.out.println("a\tdef");
         
        System.out.println("One\\t The tab length is 8");
        System.out.println("12345678def");
          
        System.out.println("Newline character \\n");
        System.out.println("abc\ndef");
 
        System.out.println("Single quotation mark \\'");
        System.out.println("abc\'def");
        System.out.println("Double quotation marks \\\"");
        System.out.println("abc\"def");
        System.out.println("Backslash itself \\");
        System.out.println("abc\\def");
    }
}

Practice: Characters in Java

Scanner reads strings from the console and converts them into character arrays
Reference conversion:

String str = "abc123";
char[] cs = str.toCharArray(); 

After converting to an array of characters, the uppercase letters and numbers in the strings read by the console are screened out and printed out.

Answer:

package character;
 
import java.util.Scanner;
 
public class TestChar {
  
    public static void main(String[] args) {
        Scanner  s = new Scanner(System.in);
        String str = s.nextLine();
        char[] cs = str.toCharArray();
         
        for (int i = 0; i < cs.length; i++) {
            char c = cs[i];
            if(Character.isUpperCase(c) || Character.isDigit(c))
                System.out.print(c);
        }
        
    }
}