我正在研究一個項目,并且我被教導在構造函數中實例化變量.我在使用ArrayList思想時遇到了一些麻煩.您能否提出一些最佳實踐,我是否需要使用實例變量定義ArrayList,或者我可以在構造函數中執行此操作.謝謝你的建議！我有一個我正在談論的內容的例子：

//imports

import java.util.*;

import java.lang.*;

public class ArrayListConstructorDemo

{

//instance variables/attributes

String string;

List list;// for example does this line need to say List list = new ArrayList();

//constructors

public ArrayListConstructorDemo()

{

String string = "null";

List list = new ArrayList();//is there anyway I can do this here instead of 6 lines up?

}//end default constructor

public ArrayListConstructorDemo(String string,List list)

{

this.string = string;

this.list = list;

}//end generic constructor

//observers/getters/accessors

public String getString(){return string;}//end method getString()

public List getList(){return list;}//end method getList()

//transformers/setters/mutators

public void setTable(String string){this.string = string;}

public void setValues(String list)

{

// for(String s : test)

// {

list.add(this.list);

// }

}

public String toString()

{

return "this is a generic toString method for the class ArrayListConstructorDemo";

}//end toString

public static void main(String[] args)

{

ArrayListConstructorDemo alcd = new ArrayListConstructorDemo();

System.out.println(alcd.list.size());

//test Lists in general

List bleh = new ArrayList();

bleh.add("b1");

System.out.println(bleh.get(0));

}//end method main()

}//end class ArrayListConstructorDemo

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