Java Development Basics ~ How to Write Programs * Exercise 1 ~

Java Development Basics ~ How to Write Programs * Exercises ~

Let's do a simple exercise using the knowledge so far.

Required knowledge

• Variables and types
• Conditional branch
• Flowchart The contents described on this page are not enough, so please try it while googled as appropriate.

Problem 1-1

Please refer to the flowchart and implement "rock-paper-scissors that only gives goo" and be sure to implement the program that you win. Please refer to this page for the judgment of winning or losing of rock-paper-scissors.

Problem 1-2

Please change "rock-paper-scissors that only produces goo" to rock-paper-scissors that only produces choki.

Problem 1-3

Please change "rock-paper-scissors that only produces goo" to ordinary rock-paper-scissors that produces other than goo. However, in this case, do not repeat and output "Aiko" as a result.

Problem 1-4

Allow your hands to enter values externally and display the results for each match. Create a rock-paper-scissors program that won't end until you win. Also, display the number of times it took to win at the end.

Answer

Problem 1-1

Janken.java

package janken;
public class Gudake {
	public static void main(String[] args) {
		//Variables that do not change once set"final"Add to make it a constant. ・ ・ ・ ①
		final int GUU=0;
		final int CHOKI=1;
		final int PA=2;
		//Set your own hands and the enemy's hands ... ②
		int myHand=PA;
		int enemyHand=CHOKI;
		//Conditional expression
		//Is it better to separate this conditional expression in terms of code? ③
		if(((myHand-enemyHand)%3)==2) {
			System.out.println("You win");
		}else {
			System.out.println("That shouldn't be the case");
		}
	}
}

Commentary)

• About the whole program As you can see in the flowchart, this time we will only consider the case of winning or losing. Please implement according to the specifications without being bound by this common sense.

• ① Apply numbers to goo, choki, and par. If you don't apply it, the program will work, but when others read it, you won't know what each number refers to. Numbers that are meaningful but you don't know what they are referring to are called magic numbers </ font>, and if you write this way, you will continue to complain. The values of goo, choki, and par this time will not be changed, so add final in front of the type to make it a constant </ b>. If you make it a constant, you cannot rewrite the value. Please rewrite it as a trial. Unlike variables, constants are written in all uppercase </ b>.

• ② Set your own hand and the enemy's hand. Write variables in camel letters (mix case like camel back). This time, you can write solid in the source code.

• ③ Make a condition judgment. The value is calculated in the if minute, but basically it is not good to put the calculation formula directly in the conditional expression ... However, this time it is a disposable sample code with only one branch. .. ..

package janken;
import java.util.Random;
public class Janken {
	public static void main(String args[]) {
		final int GUU=0;
		final int CHOKI=1;
		final int PA=2;
		int myHand=CHOKI;
		//Randomly set the opponent's hand. ・ ・ ・ ①
        Random roundom = new Random(2);
		int enemyHand=roundom.nextInt(3);
		//When writing with if ... ②
		//Calculate the winning and losing conditions in advance ... ③
		int winningResult=((myHand-enemyHand)%3);
		if(winningResult==0){
			System.out.println("I'm Aiko");
		}else if (winningResult==1) {
			System.out.println("I'm losing");
		}else {
			System.out.println("Win");
		}
		//Place to write with switch ・ ・ ・ 4
		switch((myHand-enemyHand)%3){
			case 0:
				System.out.println("I'm Aiko");
				break;
			case 1:
				System.out.println("I'm losing");
				break;
			case 2:
				System.out.println("Win");
				break;
		}
	}
}