【DataStructure】 Five methods to init the List in java

2024-07-17 11:56:45   222人阅读

Do you know how to init list in other way except for new object? The following will give you serveral tips. If having other great idea, you are welcome to share. 

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1. import java.util.ArrayList;  
2. import java.util.Arrays;  
3. import java.util.Collections;  
4. import java.util.List;  
5.   
6. public class ListUtil  
7. {  
8.   
9.     /** 
10.      *Init the List with different methods.  
11.      *  
12.      * @time Jul 21, 2014 5:39:10 PM 
13.      * @return void 
14.      */  
15.     public static void init()  
16.     {  
17.         // use new to init List  
18.         List<String> firstList = new ArrayList<String>(0);  
19.         firstList.add("ABC");  
20.         firstList.add("FGF");  
21.         firstList.add("CID");  
22.         System.out.println(firstList);  
23.           
24.         // use the string to init List  
25.         List<String> testList = Arrays.asList("ABC", "FGF", "CID");  
26.         System.out.println(testList);  
27.         //output:[ABC, ABC, GFG, CID]  
28.           
29.         /** 
30.          * Notes: The following methods is dependent on the above List. 
31.          */  
32.           
33.         //use arrays and copy to init List  
34.         List<String> copyList = Arrays.asList(new String[testList.size()]);  
35.         Collections.copy(copyList,testList);  
36.         System.out.println(copyList);  
37.           
38.         //use new object and copy to init List  
39.         copyList = new ArrayList<String>();  
40.         Collections.addAll(copyList, new String[testList.size()]);  
41.         Collections.copy(copyList,testList);  
42.         System.out.println(copyList);  
43.           
44.         //use the list.subList to init List  
45.         List<String> strSubList = testList.subList(0, testList.size());  
46.         System.out.println(strSubList);  
47.     };  
48.       
49.     public static void main(String[] args)  
50.     {  
51.         ListUtil.init();  
52.     }  
53. }  

The result is :

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1. [ABC, FGF, CID]  
2. [ABC, FGF, CID]  
3. [ABC, FGF, CID]  
4. [ABC, FGF, CID]  
5. [ABC, FGF, CID]  

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