arraylist

问题 In Java ArrayList<E> implementation base on a array of objects. Can anybody explain me why implementation of ArrayList<E> uses array Object[] for data storage instead of E[] ? What the benefit of using Object[] ? 回答1: In Java, creating an array of a generic type is not straightforward. The simple approach does not compile: public class Container<E> { E[] arr = new E[3]; // ERROR: Cannot create a generic array of E } Replace E with Object , and all is well (at the expense of added complexity

问题 In Java ArrayList<E> implementation base on a array of objects. Can anybody explain me why implementation of ArrayList<E> uses array Object[] for data storage instead of E[] ? What the benefit of using Object[] ? 回答1: In Java, creating an array of a generic type is not straightforward. The simple approach does not compile: public class Container<E> { E[] arr = new E[3]; // ERROR: Cannot create a generic array of E } Replace E with Object , and all is well (at the expense of added complexity

问题 I want to pass an ArrayList of string arrays from one activity to another in Android. How can I use intent or bundle ? Please consider that intent.putStringArrayListExtra is not working in this case, because it is not for string arrays. 回答1: Not sure what you mean by "ArrayList of string arrays" If you have string array then check the below link Passing string array between android activities http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html ArrayList implements Serializable

问题 This question already has answers here : Sort ArrayList of custom Objects by property (25 answers) Closed 5 years ago . I have a Class Student that Implements a static method public static Comparator<Student> getCompByName() that returns a new comparator object for Student that compares 2 Students objects by the attribute 'name'. I need to now test this by sorting a students ArrayList by 'name' using my function getCompByName(). Here is my Comparator method in my Student class. public static

问题 This question already has answers here : Sort ArrayList of custom Objects by property (25 answers) Closed 5 years ago . I have a Class Student that Implements a static method public static Comparator<Student> getCompByName() that returns a new comparator object for Student that compares 2 Students objects by the attribute 'name'. I need to now test this by sorting a students ArrayList by 'name' using my function getCompByName(). Here is my Comparator method in my Student class. public static

问题 Either I'm doing this wrong or i'm not understanding how this method works. ArrayList<String> a = new ArrayList<String>(); a.ensureCapacity(200); a.add(190,"test"); System.out.println(a.get(190).toString()); I would have thought that ensureCapacity would let me insert a record with an index up to that value. Is there a different way to do this? I get an IndexOutOfBounds error on the third line. 回答1: No, ensureCapacity doesn't change the logical size of an ArrayList - it changes the capacity ,

问题 I would like to remove an object from an ArrayList when I'm done with it, but I can't find way to do it. Trying to remove it like in the sample code below doesn't want to work. How could I get to the iterator of current px object in this loop to remove it? for( Pixel px : pixel){ [...] if(px.y > gHeigh){ pixel.remove(pixel.indexOf(px)); // here is the thing pixel.remove(px); //doesn't work either } } 回答1: You can't, within the enhanced for loop. You have to use the "long-hand" approach: for

问题 In Java, ArrayList and HashMap are used as collections. But I couldn't understand in which situations we should use ArrayList and which times to use HashMap . What is the major difference between both of them? 回答1: You are asking specifically about ArrayList and HashMap, but I think to fully understand what is going on you have to understand the Collections framework. So an ArrayList implements the List interface and a HashMap implements the Map interface. So the real question is when do you

问题 Right now, I have a program containing a piece of code that looks like this: while (arrayList.iterator().hasNext()) { //value is equal to a String value if( arrayList.iterator().next().equals(value)) { // do something } } Am I doing that right, as far as iterating through the ArrayList goes? The error I am getting is: java.lang.ArrayIndexOutOfBoundsException: -1 at java.util.ArrayList.get(Unknown Source) at main1.endElement(main1.java:244) at com.sun.org.apache.xerces.internal.parsers

问题 I am doing the network operation in a model and then return the result, but the arraylist size is zero when I return it but inside the onResponse method the arraylist size is not zero. How to resolve this? public class doInBackground { //i have initialized the arraylist here ArrayList<Contact> arrayList=new ArrayList<>(); String url="http://192.168.10.3/volley/allUser.php"; private Context context; public doInBackground(Context context){ this.context=context; } public ArrayList<Contact>