問題與Java的List <>

Question

我倒沒與Java列表和ArrayList熟悉..我只是需要一些工作的順利開展追加和排序。

我的算法很簡單：

set a father string 
add father to speciesList 
    mutate father to some new child 
    make this new child the future father 
    go to step 2 

的ga_和ga_struct的定義在這裏給出

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我一直在做這個

 ga_ newSpecies = new ga_(); 
     Random r= new Random(10); 
     ga_struct father= new ga_struct(); 
     father.gene="123"; 
     newSpecies.vector.add(father); 

     for (int i = 1; i < 10; i++) { 
      ga_struct ng = new ga_struct();   
      ng=newSpecies.mutate(father); 
      ng.fitness=i; 
      newSpecies.vector.add(ng); 
      father=ng;   
      System.out.println(newSpecies.vector.get(i).gene+" with fitness factor "+newSpecies.vector.get(i).fitness); 

     } 

     newSpecies.sortspecies(); 
     System.out.println("\ncurrent population\n"); 

     for (int i = 0; i < 10; i++) { 
      System.out.println(newSpecies.vector.get(i).gene+" with fitness factor "+newSpecies.vector.get(i).fitness); 
     } 

增變函數只是改變一次只能有一個角色。我在第一個循環中從「父親」突變了9個新物種。但是..我不知道爲什麼代碼的輸出是給我這個 -

133 with fitness factor 1 
433 with fitness factor 2 
433 with fitness factor 3 
443 with fitness factor 4 
453 with fitness factor 5 
553 with fitness factor 6 
563 with fitness factor 7 
563 with fitness factor 8 
573 with fitness factor 9 

current population 

573 with fitness factor 9 
573 with fitness factor 9 
573 with fitness factor 9 
573 with fitness factor 9 
573 with fitness factor 9 
573 with fitness factor 9 
573 with fitness factor 9 
573 with fitness factor 9 
573 with fitness factor 9 
573 with fitness factor 9 

第一個循環是證明突變會慢慢..我也有突變後立即加入，那麼爲什麼後來所有這些都被最新版本覆蓋了？

Answer 1

首先，您的對象使用有點奇怪。

在變異中，你似乎在改變和回報父親。

這意味着您的列表將包含對同一實例的多個引用。

澄清：

public ga_struct mutate(ga_struct parent) //takes in reference to parent 
{ 
    Random r= new Random(); //modifies parent 
    ......  do some modification to the parent 
    return parent; //return reference to parent 
} 

而在你的主：

ga_ newSpecies = new ga_(); 
    Random r= new Random(10); 
    ga_struct father= new ga_struct();//instantiate father 
    father.gene="123"; 
    newSpecies.vector.add(father); 

    for (int i = 1; i < 10; i++) { 
     ga_struct ng = new ga_struct();//create new instance for child 
     ng=newSpecies.mutate(father);//set ng as reference to same instance as father, instance instantiated on previous line is discarded 
     ng.fitness=i; 
     newSpecies.vector.add(ng); 
     father=ng;   
     System.out.println(newSpecies.vector.get(i).gene+" with fitness factor "+newSpecies.vector.get(i).fitness); 

    } 

更多類似這樣的勇於嘗試：

public ga_struct mutate(ga_struct parent) 
{ 
    ga_struct ng = new ga_struct(); 
    ng.gene = father.gene; 
    Random r= new Random(); 
    //do some modification to ng 
    return ng; 
} 

，並在您的主：

a_ newSpecies = new ga_(); 
    Random r= new Random(10); 
    ga_struct father= new ga_struct(); 
    father.gene="123"; 
    newSpecies.vector.add(father); 

    for (int i = 1; i < 10; i++) {  
     ga_struct ng=newSpecies.mutate(father); 
     ng.fitness=i; 
     newSpecies.vector.add(ng); 
     father=ng;   
     System.out.println(newSpecies.vector.get(i).gene+" with fitness factor "+newSpecies.vector.get(i).fitness); 

    } 

    newSpecies.sortspecies(); 
    System.out.println("\ncurrent population\n"); 

    for (int i = 0; i < 10; i++) { 
     System.out.println(newSpecies.vector.get(i).gene+" with fitness factor "+newSpecies.vector.get(i).fitness); 
    } 

Answer 2

你與單個對象到處工作，你從來沒有一個新的ga_struct實例添加到列表中。你mutate()方法看起來簡單修改parent參數，並返回它 - 它仍然是相同的對象，只是修改，這意味着它無處不修改。

public ga_struct mutate(ga_struct parent) 
{ 
    Random r= new Random(); 
    ......  do some modification to the parent 
    return parent; 
} 

你做創建的ga_struct一個新的實例，但是你馬上通過設置參考突變father（這仍然是相同的實例，只是修改）覆蓋它：在

for (int i = 1; i < 10; i++) { 
     ga_struct ng = new ga_struct();   
     ng=newSpecies.mutate(father); //the new ga_struct is overwritten 
     ng.fitness=i; 
     newSpecies.vector.add(ng); 
     father=ng;   
     System.out.println(newSpecies.vector.get(i).gene+" with fitness factor "+newSpecies.vector.get(i).fitness); 

    } 

你的輸出此循環似乎工作，因爲您看到按其發生順序對father所做的修改。 但是，你實際上做的是隻需添加引用相同的（修改）對象遍地到List。

因此，當您最終全部打印出來時，您會在List中看到10個重複條目。

---

我的建議是要改變mutate()返回的ga_struct一個新的實例 - 你可以創建一個新對象，並設置它的gene場是從parent突變gene領域。或者你可以cloneparent和然後改變克隆的基因串。在這兩種情況下，你最終將返回的ga_struct一個新的實例應該解決這個問題。

public ga_struct mutate(ga_struct parent) 
{ 
    Random r= new Random(); 
    ga_struct mutant = parent.clone(); 
    //or 
    //ga_struct mutant = new ga_struct(); 
    //mutant.gene = parent.gene; 

    ......  do some modification to the mutant 
    return mutant; //now you'll be returning a new object not just a modified one 
} 

Answer 3

您並未創建新對象，您已將父對象添加到向量9次。

你已經有了本質是什麼

父親 - > OBJ @ 123

您列出對象的樣子是 [OBJ @ 123，OBJ @ 123，OBJ @ 123，...]

您將需要創建新的實例來記錄它。我會建議實施「克隆（）」方法來做到這一點。