java - 创建 <Fish> arrayList 深拷贝

Question

无论出于何种原因，当我尝试为植物数组列表创建深拷贝时，我收到一个空指针异常，但我不知道为什么。

/**
 * Copy Constructor. Since landscape is immutable in the scope of our
 * project, you could do a simple reference copy for it. However, Fish and
 * Plants are mutable, so those lists must be copied with a DEEP copy! (In
 * other words, each fish and each plant must be copied.)
 */



private ArrayList<Fish> fish;
private ArrayList<Plant> plants;
private int[][] landscape;

public Model(Model other) {
    this.landscape = other.landscape;

    for(Fish fishy: other.fish){
        this.fish.add(new Fish(fishy));
    }

    for(Plant planty: other.plants){
        this.plants.add(new Plant(planty));
    }
}

Answer 1

您还没有初始化鱼和植物

public Model(Model other) {
    fish = new ArrayList<Fish>();
    plants = new ArrayList<Plant>();
    this.landscape = other.landscape;

    for(Fish fishy: other.fish){
        this.fish.add(new Fish(fishy));
    }

    for(Plant planty: other.plants){
        this.plants.add(new Plant(planty));
    }
}