Question

当我尝试应用GA算法时，我发现了一个问题：我将列表A的值复制到另一个B，然后我操纵了B.但是当我运行单元测试时。我只是发现A和B的值都发生了变化。我不知道发生了什么。以下是我的代码：

public class GA_bags {
    private Population population;
    private int fittest;
    private List<Individual> offsprings;

public GA_bags(int n,int sumBags,int maxWeight,Bag[] bags){
    this.population=new Population(n,sumBags,maxWeight,bags);
}


//Crossover Function
public void crossover(){
    Random random=new Random();
    List<Individual> individuals=population.getIndividuals();
    offsprings=new ArrayList<>(individuals);    //Intialize the offsprings, simply copy first
    int pos=random.nextInt(offsprings.get(0).getGenes().length);    //decide the position of genes to crossover
    for(int i=0;i<offsprings.size()-1;i+=2){         //1st fittest pair with 2nd fittest,3nd with the 4th...
        for(int j=0;j<=pos;j++){
            int tem=offsprings.get(i).getGenes()[j];
            offsprings.get(i).getGenes()[j]=offsprings.get(i+1).getGenes()[j];
            offsprings.get(i+1).getGenes()[j]=tem;
        }
    }
}

实现交叉方法后，List个体和后代都发生了变化，但我只是操纵了List offsprings。

public class Individual {
//each individual is a solution of KnapsackProblem
private int[] genes;      //"1" stands for the bag is chosen, while "0" stands for the bag is not
private Bag[] bags;       //each digit of gene is responsible for a specific Bag object
private int fitness;     //the fitness of an individual
private int curWeight;   //the weight of this individual
private int maxWeight;   //once the total weight of bags of this individual over maxWeight, then fitness is 0

public Individual(int sumBags,int maxWeight,Bag[] bags){
     this.genes=new int[sumBags];
     this.maxWeight=maxWeight;
     this.bags=bags;
     Random random=new Random();
     for(int i=0;i<sumBags;i++){
         genes[i]=random.nextInt(2);       //genetic code: random generate genes,"0" or "1"
     }
 }
}

Answer 1

关于深层复制，here就是一个例子。

如果要复制基元类型，可以使用=。如果要复制对象，=只是使变量指向对象地址。所以这两个变量都指向同一个对象。

如果您想要新的变量指向一个全新的对象，您需要自己复制它。最简单的方法是逐个复制原始属性。

为什么我没有操作的对象在Java中被改变了？

1 个答案: