乱数の生成 Math.random();

public class Lesson036{
    public static void main(String args[]){
        //randomメソッドは実数を生成するのでdouble型の変数を宣言
        double d;
        //randomメソッドで生成した実数を変数dに代入
        d = Math.random();
        //出力
        System.out.println(d);
    }
}

整数を生成する場合 (int)(Math.random()*10)

public class Lesson037{
    public static void main(String args[]){
        //int型変数iを宣言
        int i;
        //randomメソッドで0以上10未満の整数を生成
        i = (int)(Math.random()*10);
        //出力
        System.out.println(i);
    }
}

代入演算子

class JSample10_1{
  public static void main(String[] args){
    int num;

    num = 10;
    System.out.println(num);
    num += 5;
    System.out.println(num);//15

    num = 8;
    System.out.println(num);
    num *= 4;
    System.out.println(num);//32
  }

配列データ型[] 配列変数名 = new データ型[要素数]

int [] num = {1,2,3,4,5,};

int[] num = new int[5];

class JSample2_1{
  public static void main(String[] args){
    int[] result = new int[3];

    result[0] = 75;
    result[1] = 88;
    result[2] = 82;

    for (int i = 0 ; i < 3 ; i++){
      System.out.println(result[i]);
    }
  }
}

拡張for文 for (データ型変数名: コレクション)

String name[] = {"Suzuki", "Katou", "Yamada"};

for (String str: name){
  System.out.println(str);
}

標準入力　Scanner scan = new Scanner(System.in);

import java.util.Scanner;
 
public class InputSample {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String str1 = scan.nextLine();//行入力を取得
        String str2 = scan.next();//空白文字までを取得
        int num = scan.nextInt();//数値を取得
        System.out.println(str1);
        System.out.println(str2);
        System.out.println(num);
        scan.close();
    }
}

戻り値

class JSample5_1{
  public static void main(String args[]){
    int kekka;

    kekka = bai(9);
    System.out.println(kekka);

    kekka = bai(5);
    System.out.println(kekka);
  }

  private static int bai(int n){
    return n * 2;
  }
}