java数组初始化不正确。BasicDBObject无法创建BasicDBObject类型的数组

Question

case 3:
    BasicDBObject []document= new BasicDBObject(); // error             
    DBCollection table1 = db.getCollection("user");
    document[0].put("name", "mkyong");
    document[0].put("age", 30);
    table1.insert(document);
    System.out.println("Collection Inserted successfully");
    break;

不了解初始化的问题

Answer 1

由于数组初始化不正确，您将得到编译时错误

BasicDBObject []document= new BasicDBObject(); //error

java中的基本数组初始化如下

Object objectArr[] = new Object[10];

因此，您必须初始化数组，并以下面的方式传递值

BasicDBObject []document1= new BasicDBObject[2];

document1[0] = new BasicDBObject();
document1[0].put("name", "mkyong12");
document1[0].put("age", 30);

document1[1] = new BasicDBObject();
document1[1].put("name", "test12");
document1[1].put("age", 44);

您必须确保每个数组对象都应该初始化，否则会导致NullPointerException失败

希望这有帮助

Answer 2

您可以使用^{}：

BasicDBObject document = new BasicDBObject();
document.put("name", "mkyong");
document.put("age", 30);

BasicDBList documentList = new BasicDBList();
documentList.add(document);

DBCollection table1 = db.getCollection("user");
table1.insert(documentList.get(0));
System.out.println("Collection Inserted successfully");

Answer 3

insert方法接受一个DBObject

BasicDBObject document= new BasicDBObject();
document.put("name", "mkyong");
document.put("age", 30);
table1.insert(document);