Java 如何迭代HashMap<;字符串,ArrayList<;汽车>&燃气轮机;
如何从HashMap打印ArrayListJava 如何迭代HashMap<;字符串,ArrayList<;汽车>&燃气轮机;,java,hashmap,Java,Hashmap,如何从HashMap打印ArrayList Map<String, ArrayList<Car>> cars = new HashMap<String, ArrayList<Car>>; ArrayList<Car> carList = cars.get("bmw"); for (int i = 0; i < carList.size(); i++) { System.out.println(carLi
Map<String, ArrayList<Car>> cars = new HashMap<String, ArrayList<Car>>;
ArrayList<Car> carList = cars.get("bmw");
for (int i = 0; i < carList.size(); i++) {
System.out.println(carList.get(i));
}
尽管“bmw”密钥存在并已填充。尝试添加一个
System.out.println(cars.get("bmw"));
要查看列表中的确切内容(在地图和汽车列表中)。遍历列表的最简单方法是使用foreach:
ArrayList<Car> carList = cars.get("bmw");
for (Car car : carList) {
System.out.println(car.getYourValueToPrint());
}
ArrayList carList=cars.get(“宝马”);
用于(汽车:carList){
System.out.println(car.getYourValueToPrint());
}
迭代ArrayList最安全的方法是通过增强for each循环,从而避免出现NullPointerException
:
ArrayList<Car> carList = cars.get("bmw");
for(Car car: carList){
car.doAnyOpertation();
System.out.println(car.getAnyValue());
}
ArrayList carList=cars.get(“宝马”);
用于(汽车:carList){
car.doAnyOperation();
System.out.println(car.getAnyValue());
}
ArrayList carList=cars.get(“宝马”);
用于(汽车:carList){
car.doAnyOperation();
System.out.println(car.getAnyValue());
}
即使在这种情况下,如果carList为null,则第行for(Car-Car:carList)
with-throw-NPE为什么不使用iterator
?比iterator
好得多的是增强的for循环(假设您使用的是JDK 1.5或更高版本)。啊。。密钥应以大写字母开头。谢谢:)
carList.add("Some value");
ArrayList<Car> carList = cars.get("bmw");
for (Car car : carList) {
System.out.println(car.getYourValueToPrint());
}
ArrayList<Car> carList = cars.get("bmw");
for(Car car: carList){
car.doAnyOpertation();
System.out.println(car.getAnyValue());
}
ArrayList<Car> carList = cars.get("bmw");
for(Car car: carList){
car.doAnyOpertation();
System.out.println(car.getAnyValue());
}