[Java] Baekjun number 2557 - Hello World

BaekJoon 2557

Solution

public class Main {
    public static void main(String args[]) {
        System.out.print("Hello World!");
    }
}

For Java in Baekjun

public class Main {
	public static void main(String args[]) {
    }
}

You should write the main method as follows:

• The main method operates first when running a Java application (main), can be accessed from any object (public), is defined the moment Java is compiled (static), and is a function that does not return a value (void).

As I usually solve problems using programmers, I was confused because often I just had to put the answer in the answer.

main method in java

• Because program startup is the main method, when a Java application is executed, the main method is executed first. public: Access modifier, means the object can be referenced from anywhere.
• A type of restriction that can be accessed from the outside
• The types are in the order of strongest constraints: private -> protected -> public default: Can be accessed from the same package as inside the class static: This means that this function is a static function. If a function or class is declared with static, the corresponding object is defined the moment Java is compiled -> Afterwards, objects other than static are defined.
  • Therefore, it is impossible to call an object other than static from a static object.
  • Because static is defined first, objects that have not yet been defined cannot be called. void: Only executes, no return value -> Just moves to the called part after the function ends. String args[]: Used to receive values from outside when executing a program.

    java Main hello 123
    

    public static void main(String[] args) {
      System.out.println(args[0]); // hello
      System.out.println(args[1]); // 123
    }
    

  • The received hello and 123 values are entered into the args array.
  • In KOTE, input is mostly received through Scanner and BufferedReader, so it is rarely used.

Output from java

print: simply prints the content in parentheses printf: Same as printf in C, used to write %d, %s, etc. println: After printing the content in parentheses, a newline character (\n) is included at the end, leaving a single line space after printing.