arraylist | 易学教程

ArrayList capacity size increasing strange behaviour

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问题 When ArrayList wants to store more elements than actual capacity it increases the capacity. It is very cost efficient operation since we actually copy all data from previous ArrayList to new ArrayList with larger capacity. However I wonder that maybe some operations with capacity are not proceeded when ArrayList just needs more space - but much before. I wonder what takes such long time for "slow indexes" from my output and increasing capacity is my only one idea. Here is my code: import java

Sync multiple source ArrayLists into single target list

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问题 There is a requirement to load a list of items(ArrayList) from two different tables. Due to complex Hibernate mapping, they can not be loaded as one ArrayList. So they are loaded separately by two different Hibernate bags in the class definition. When I use them I'd like to combine into single list. So I am thinking about writing a function as follows, private List<Item> combinedList = new ArrayList<Item>(); public List<Item> getCombinedList() { combinedList.clear(); combinedList.addAll

How to iterate a list inside a list in java?

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问题 Hi i have two value object classes . package org.array; import java.util.List; public class Father { private String name; private int age ; private List<Children> Childrens; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public List<Children> getChildrens() { return Childrens; } public void setChildrens(List<Children> childrens) { Childrens = childrens; } }

Instantiating a new arraylist then adding to the end of it

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问题 public ArrayList<Person> people; Is this how you would instantiate the people variable as a new empty ArrayList of Person objects? ArrayList<Person> people = new ArrayList<Person>(); And is this how you would add newMember to the end of the list? public void addItem(Person newMember){ people.add(newMember); } 回答1: No class Foo { public ArrayList<Person> people; Foo() { //this: ArrayList<Person> people = new ArrayList<Person>(); //creates a new variable also called people! System.out.println

Passing and ArrayList<Service> through intent

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问题 I have a class called Service, which is used to create Service objects using this constructor public Service(int id, String service_name, String service_code) { this.id = id; this.service_name = service_name; this.service_code = service_code; } then I create a list call service list as with the following signature List<Service> serviceList = new ArrayList<Service> I have try to pass this ArrayList through Intent Object like this Intent i = new Intent(Classname.this, anotherClass.class); i

Removing the smallest 2 elements in an arraylist in java?

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问题 I have an arraylist of integers, i need to compute the average of the integers excluding the smallest two integers. I keep trying different ways of doing this but think what I want to do is find min1, remove it and then find min2 then remove that. public double computeAverageWithoutLowest2() { ArrayList<Student> newscores = new ArrayList<Student>(scores); int newtotalScores=0; int newavg=0; int min1 = 0; int min2 = 0; min1 = newscores.get(0).getScore(); for (int i = 0; i< newscores.size(); i+

Comparing students according to score JAVA

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问题 I have a class of Student. The class has String name , int studentId and int studentScore . I want to compare the students in ArrayList<Student> students according to the studentscore. This means if "student 1" and "student 2" has the same amount of studentscore then both of their ranks will be the same. I have a function where I set The rank. But I'm unsure how to compare everything in the arraylist. When I search for comparing int values I get the results: How to properly compare two

How can i write an array that holds multiple values for each product

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问题 I've been searching around php.net, w3schools and youtube for something that has multiple objects like "move1, movie2" where each of those objects has variables like "id, qty, price" . I prefer an array were I can leave the qty value empty so I can have the user input it though a <form> , but I will figure that out once I find a form that fits what I need. Any kind of help would be much appreciated. I just need a look at the kind of array I need and if I will be able to apply it to my code

java第六次作业

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（一）学习总结 1.用思维导图对本周的学习内容进行总结。 2.当程序中出现异常时，JVM会依据方法调用顺序依次查找有关的错误处理程序。可使用printStackTrace 和getMessage方法了解异常发生的情况。阅读下面的程序，说明printStackTrace方法和getMessage方法的输出结果分别是什么？并分析异常的传播过程。 public class PrintExceptionStack { public static void main( String args[] ) { try { method1(); } catch ( Exception e ) { System.err.println( e.getMessage() + "\n" ); e.printStackTrace(); } } public static void method1() throws Exception { method2(); } public static void method2() throws Exception { method3(); } public static void method3() throws Exception { throw new Exception( "Exception thrown in method3" ); } }

Java ArrayList and LinkedList - adding element at end implementation details

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问题 My understanding of why arraylist is faster than a linkedlist is that with an arraylist you basically only need one action - update the reference at the end array element, whereas with a linked list you have to do much more e.g. create a new node, update 2 references, go through linked list and update the last node to point to the new one etc. However I am not sure how java implement these. How does the arraylist know where the "last" element is, does it store a value of the last element or