筋トレ大好きな文系女学生のJava入門_静的メンバ ref: http://qiita.com/amippy/items/cc150d4b64aaf53ee730

file0.java

1 public class Main{
2  public static void main(String[] args){
3     MuscleBoy mb1 = new MuscleBoy();
4     mb1.hp = 100;
5     MuscleBoy mb2 = new MuscleBoy();
6     mb2.hp = 70;
7     }
8 }

file1.java

1 public class MuscleBoy{
2   int hp;
3   String name;
4   int money;
5 }

file2.java

1 public class MuscleBoy{
2  int hp;
3  String name;
4  static int money;　　　　　　　　　　　//静的フィールド
5 }

file3.java

1 public class Main{
2  public static void main(String[] args){
3    MuscleBoy mb1 = new MuscleBoy();
4    MuscleBoy mb2 = new MuscleBoy();
5    System.out.println(mb1.name);
6    System.out.println(MuscleBoy.money);  
7  }
8 }

file4.java

1 public class Main{
2  public static void main(String[] args){
3    MuscleBoy mb1 = new MuscleBoy();
4    MuscleBoy mb2 = new MuscleBoy();
5    MuscleBoy.money = 1000;
6    System.out.println(MuscleBoy.money);  //1000と表示
7    System.out.println(mb1.money);   //1000と表示
8    mb1.money = 2000;　　　　　　　　　//mb1に2000を代入
9    System.out.println(mb2.money);  //mb2.moneyでも2000と表示
10  }
11 }

file5.java

1 public class Main{
2  public static void main(String[] args){
3    //１人も筋肉ボーイを生み出していない状況
4    MuscleBoy.money = 1000;
5    System.out.println(MuscleBoy.money);
6 }
7}

file6.java

1 public class MuscleBoy{
2  int hp;
3  String name;
4  static int money;
5
6  static void setRandomMoney(){       //staticをつけたメソッド
7    MuscleBoy.money = (int) (Math.random() * 1000);
8   }
9 }

file7.java

1 public class Main{
2   public static void main(String[] args){
3    MuscleBoy.setRandomMoney();
4    System.out.println(MuscleBoy.money);   //ランダムな金額が表示される
5    MuscleBoy mb1 = new MuscleBoy();
6    System.out.println(mb1.money);     //同じ金額を表示
7   }
8 }