#멋쟁이사자처럼 #부트캠프 #백엔드 #JAVA

String Concatenation

When a value is added to a string, it automatically gets converted to a string.

String str = "hello";
int i = 10;

System.out.println(str + i + i); // hello1010

Practice: Multiplication Table

public class Practice01 {
    public static void main(String[] args) {
        for (int i = 1; i < 10; i++) {
            for (int dan = 2; dan < 10; dan++) {
                System.out.print(dan + "*" + i + " = " + (dan * i) + "   \\\\t");
            }
            System.out.println();
        }
    }
}

2*1 = 2   	3*1 = 3   	4*1 = 4   	5*1 = 5   	6*1 = 6   	7*1 = 7   	8*1 = 8   	9*1 = 9   	
2*2 = 4   	3*2 = 6   	4*2 = 8   	5*2 = 10   	6*2 = 12   	7*2 = 14   	8*2 = 16   	9*2 = 18   	
2*3 = 6   	3*3 = 9   	4*3 = 12   	5*3 = 15   	6*3 = 18   	7*3 = 21   	8*3 = 24   	9*3 = 27   	
2*4 = 8   	3*4 = 12   	4*4 = 16   	5*4 = 20   	6*4 = 24   	7*4 = 28   	8*4 = 32   	9*4 = 36   	
2*5 = 10   	3*5 = 15   	4*5 = 20   	5*5 = 25   	6*5 = 30   	7*5 = 35   	8*5 = 40   	9*5 = 45   	
2*6 = 12   	3*6 = 18   	4*6 = 24   	5*6 = 30   	6*6 = 36   	7*6 = 42   	8*6 = 48   	9*6 = 54   	
2*7 = 14   	3*7 = 21   	4*7 = 28   	5*7 = 35   	6*7 = 42   	7*7 = 49   	8*7 = 56   	9*7 = 63   	
2*8 = 16   	3*8 = 24   	4*8 = 32   	5*8 = 40   	6*8 = 48   	7*8 = 56   	8*8 = 64   	9*8 = 72   	
2*9 = 18   	3*9 = 27   	4*9 = 36   	5*9 = 45   	6*9 = 54   	7*9 = 63   	8*9 = 72   	9*9 = 81  

Label

abc: for (;;) {
    for (;; i++) {
        if (i == 255) {
            break abc;
        }
    }
}
System.out.println("Noww i am back");

Ways to Initialize An Array

// Declaration and Initialization in One Line
int[] arr1 = {1,2,3,4,5};

// Declaration and Initialization Separately
int[] arr2 = new int[5];
arr2[0] = 1;
arr2[1] = 2;
arr2[2] = 3;
arr2[3] = 4;
arr2[4] = 5;

// Using an Array Initializer
int[] arr3 = new int[]{1, 2, 3, 4, 5};

// Initializing with Default Values
int[] arr4 = new int[5];

Practice: For-each loop

import java.util.TreeSet;

public class Main {
    public static void main(String[] args) {
        TreeSet<Integer> numbers = new TreeSet<>();

        for (int i = 0; i < 5; i++) {
            numbers.add(i);
            numbers.add(i);
        }

        for (Integer item : numbers) {
            System.out.println(item);
        }
    }
}

Class Arrays