數組返回空值

Question

我對Arrays感到有些困惑，希望有人可以幫助我。

我希望這是有道理的，因為我有些困惑。 任何幫助深表感謝！

while循環在“聯盟”類中創建對象

     while (lineScanner.hasNextLine())
       {
       currentLine = lineScanner.nextLine();
           String[] newSSs = currentLine.split(","); 
           Team team = new Team(newSS[0]);
           team.setWins(Integer.valueOf(newSS[1]));
           team.setDraws(Integer.valueOf(newSS[2]));
           team.setLoses(Integer.valueOf(newSS[3]));
           team.setPoints(team.calculatePoints());

Answer 1

我想我知道您要做什么...在while循環之前創建一個ArrayList（您需要某種類型的集合來存儲已分析的團隊）：

private ArrayList<Team> teams = new ArrayList<Team>();

while (lineScanner.hasNextLine()){
    currentLine = lineScanner.nextLine();
    String[] newSSs = currentLine.split(","); 
    Team team = new Team(newSS[0]);
    team.setWins(Integer.valueOf(newSS[1]));
    team.setDraws(Integer.valueOf(newSS[2]));
    team.setLoses(Integer.valueOf(newSS[3]));
    team.setPoints(team.calculatePoints());
}

您實際上只有一個陣列-一個可容納團隊的陣列。 newSS的生命周期僅限於循環一次，一旦lineScanner沒有更多要處理的行，則循環結束，並丟棄newSS。

希望對您有所幫助

Answer 2

我猜：

  ArrayList<Team> list = new ArrayList<Team>();
  for(int i=0;i<5;i++)
     list.add(null);

   //change values
    list.set(0,new Team(newSS[0]);
    list.get(0).setWins(Integer.valueOf(newSS[1]));

Answer 3

我認為您的Team類具有以下方法-

setWins()
setDraws()
setLoses()
setPoints()  

但是在這里，您嘗試使用這些方法組成一個已聲明為數組的Team team team-

Team team = new Team(newSS[0]); 

由於此處的team是一系列Team嘗試執行以下操作-

team[0].setWins(Integer.valueOf(newSS[1]));
team[0].setDraws(Integer.valueOf(newSS[2]));
team[0].setLoses(Integer.valueOf(newSS[3]));

Answer 4

從代碼片段來看，您似乎希望將團隊詳細信息存儲在Team對象中。 但是，您有許多Team對象，並且需要它們的數組。 這很接近：

ArrayList<Team> teamList = new ArrayList<Team>();
while (lineScanner.hasNextLine())
   {
   currentLine = lineScanner.nextLine();
       String[] newSSs = currentLine.split(","); 
       Team team = new Team(newSS[0]);
       team.setWins(Integer.valueOf(newSS[1]));
       team.setDraws(Integer.valueOf(newSS[2]));
       team.setLoses(Integer.valueOf(newSS[3]));
       team.setPoints(team.calculatePoints());
teamList.add(team);
}

Java 7 ArrayList Java 8 ArrayList