arraylist

java reading from csv file and storing its information into ArrayList<class>

由 爱⌒轻易说出口 提交于 2019-12-17 16:51:52
问题 I'm a java newbie and I need a some help so here is my main method: RegistrationMethods dmv = new RegistrationMethods(); ArrayList<CarOwner> ItState = new ArrayList<CarOwner>(); dmv.processTextToArrayList(ItState); and I have a class called CarOwner and it has getters and setters for firstName, lastName, license, month, year instance variables. And this is my method header for processTextToArrayList method: public void processTextToArrayList(ArrayList<CarOwner> inList) throws IOException this

Why the maximum array size of ArrayList is Integer.MAX_VALUE - 8?

由 自闭症网瘾萝莉.ら 提交于 2019-12-17 16:43:39
问题 I am studying Java 8 documentation for ArrayList . I got that maximum array size is defined as Integer.MAX_VALUE - 8 means 2^31 – 8 = 2 147 483 639 . Then I have focused on why 8 is subtracted or why not less than 8 or more than 8 is subtracted? /** * The maximum size of array to allocate. * Some VMs reserve some header words in an array. * Attempts to allocate larger arrays may result in * OutOfMemoryError: Requested array size exceeds VM limit */ private static final int MAX_ARRAY_SIZE =

When you call remove(object o) on an arraylist, how does it compare objects?

由 纵饮孤独 提交于 2019-12-17 16:31:53
问题 When you call remove(object o) on an arraylist in java, how does it compare the objects to find the correct one to remove? does it use the pointer? or does it compare the objects using the interface Comparable? 回答1: ArrayList remove() relies on the objects implementation of the Equal method. If no implementation has been done then the object is removed by Object 's implementation of Equals which indeed is the pointer comparison. From the documentation on ArrayList - More formally, removes the

ArrayList Generic without Type

由 别来无恙 提交于 2019-12-17 16:26:26
问题 recently I read a piece of code which seems weird to me. As we know, we need to initialize the generic type in collections when we need to use them. Also, we know Collections can contain Collections as their elements. The code: public class Solution { public static void main(String args[]) { ArrayList res = returnlist(); System.out.print(res.get(0)); } public static ArrayList<ArrayList<Integer>> returnlist() { ArrayList result = new ArrayList(); ArrayList<Integer> content = new ArrayList

java集合List解析

由 时光怂恿深爱的人放手 提交于 2019-12-17 16:25:51
作为一个Developer，Java集合类是我们在工作中运用最多的、最频繁的类。相比于数组(Array)来说，集合类的长度可变，更加适合于现代开发需求； Java集合就像一个容器，可以存储任何类型的数据，也可以结合泛型来存储具体的类型对象。在程序运行时，Java集合可以动态的进行扩展，随着元素的增加而扩大。在Java中，集合类通常存在于java.util包中。 Java集合主要由2大体系构成，分别是Collection体系和Map体系，其中Collection和Map分别是2大体系中的顶层接口。 Collection主要有三个子接口，分别为List(列表)、Set(集)、Queue(队列)。其中，List、Queue中的元素有序可重复，而Set中的元素无序不可重复； List中主要有ArrayList、LinkedList两个实现类；Set中则是有HashSet实现类；而Queue是在JDK1.5后才出现的新集合，主要以数组和链表两种形式存在。 Map同属于java.util包中，是集合的一部分，但与Collection是相互独立的，没有任何关系。Map中都是以key-value的形式存在，其中key必须唯一，主要有HashMap、HashTable、TreeMap三个实现类。 1 List 在Collection中，List集合是有序的

Java ArrayList IndexOf - Finding Object Index

由 ◇◆丶佛笑我妖孽 提交于 2019-12-17 16:07:21
问题 Lets say I have a class public class Data{ public int k; public int l; public Data(int k, int l){ this.k = k; this.l = l; } public boolean equals(Date m){ if(this.k == m.k && this.l = m.l) return true; return false; } } And I add a few Data objects to a ArrayList: ArrayList<Data> holder = new ArrayList<Data>; Data one = new Data(0,0); Data two = new Data(0,4); Data three = new Data(0,5); Why does indexOf not find this?: holder.indexOf(new Data(0,4)); //returns -1 Is indexOf any better than

Android Spinner databind using array list

由 99封情书 提交于 2019-12-17 15:59:13
问题 I have a array list like this: private ArrayList<Locations> Artist_Result = new ArrayList<Location>(); This Location class has two properties: id and location . I need to bind my ArrayList to a spinner. I have tried it this way: Spinner s = (Spinner) findViewById(R.id.SpinnerSpcial); ArrayAdapter adapter = new ArrayAdapter(this,android.R.layout.simple_spinner_item, Artist_Result); s.setAdapter(adapter); However, it shows the object's hexadecimal value. So I think I have to set display the

Why is vector array doubled?

由 微笑、不失礼 提交于 2019-12-17 15:42:22
问题 Why does the classic implementation of Vector (ArrayList for Java people) double its internal array size on each expansion instead of tripling or quadrupling it? 回答1: When calculating the average time to insert into a vector, you need to allow for the non-growing inserts and the growing inserts. Call the total number of operations to insert n items o total , and the average o average . If you insert n items, and you grow by a factor of A as required, then there are o total = n + ΣA i [ 0 < i

Java generics - ArrayList initialization

由 故事扮演 提交于 2019-12-17 15:29:00
问题 It is known that arraylist init. should be like this ArrayList<A> a = new ArrayList<A>(); ArrayList<Integer> a = new ArrayList<Number>(); // compile-time error so, why does java allow these ? 1. ArrayList<? extends Object> a1 = new ArrayList<Object>(); 2. ArrayList<?> a2 = new ArrayList<Integer>(); then, if they are correct why doesn't allow these ? 1. a1.add(3); 2. a2.add(3); the compiler message is : The method add(int, capture#1-of ? extends Object) in the type ArrayList is not applicable

How can I create a list Array with the cursor data in Android

由 假装没事ソ 提交于 2019-12-17 15:27:29
问题 How can I create a list Array (the list display First Alphabet when scroll) with the cursor data? 回答1: Go through every element in the Cursor , and add them one by one to the ArrayList . ArrayList<WhateverTypeYouWant> mArrayList = new ArrayList<WhateverTypeYouWant>(); for(mCursor.moveToFirst(); !mCursor.isAfterLast(); mCursor.moveToNext()) { // The Cursor is now set to the right position mArrayList.add(mCursor.getWhateverTypeYouWant(WHATEVER_COLUMN_INDEX_YOU_WANT)); } (replace
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