Constructor 1 « Constructor « Java Class Q&A

Java Class Q&A
1.abstract class
2.Base class
3.class hierarchy
4.class name
5.class version
14.equal method
15.extend Class
19.inner class
21.main class
26.object reference
28.parent class
31.Private Field
35.Static Class
39.Wrapper Class
Java Class Q&A » Constructor » Constructor 1 

1. How do I call one constructor from another in Java?

Is it possible to call a constructor from another (within the same class, not from a subclass)? If yes how? And what could be the best way to call another constructor ...

2. Are varargs allowed in a java enum constructor?

enum MyEnum {
  A( 1, 2, 3, 4),
  B(1, 2),
  C(4, 5, 8, 8, 9);

 private MyEnum( int firstInt, int... otherInts ) {
  // do something with ...

3. Why might one also use a blank constructor?

I was reading some Java recently and came across something (an idiom?) new to me: in the program, classes with multiple constructors would also always include a blank constructor. For example: ...

4. Use of the String(String) constructor in Java

I've read on articles and books that the use of String s = new String("..."); should be avoided pretty much all the time. I understand why that is, but is ...

5. Why must delegation to a different constructor happen first in a Java constructor?

In a constructor in Java, if you want to call another constructor (or a super constructor), it has to be the first line in the constructor. I assume this is ...

6. How much code should one put in a constructors (Java)?

I was thinking how much code one should put in constructors in Java? I mean, very often you make helper methods, which you invoke in a constructor, but sometimes there are ...

7. Java Constructors

I am trying to learn how to specify class constructors in Java. I am starting to understand that they specify the types of instance variables of objects made from that class. ...

8. Use of Initializers vs Constructors in Java

So I've been brushing up on my Java skills as of late and have found a few bits of functionality that I didn't know about previously. Static and Instance Initializers are ...

9. constructor problem in java

public class StateQueryFilter extends FieldQueryFilter {
   // private static final Log LOG = LogFactory.getLog(RecommendedParser.class.getName());

    public StateQueryFilter() {
        super("state", 5f);

10. Is there any justifiable reason to use new and a constructor on a number class in Java?

Is there any justifiable reason to in Java something like

Long l = new Long(SOME_CONSTANT)
This creates an extra object and is tagged by FindBugs, and is obviously a bad practice. My ...

11. What is this constructor call with following double braces?

Unfortunately I haven't coded Java for about five years and I absolutely can not remember how or why the following code is working. I stumbled across a similar example and broke it ...

12. Custom class loader in Constructor.newInstance

I'm using rhino via the bean scripting framework to create and configure objects in my java process. Some of the classes used in the scripts need to be loaded dynamically as ...

13. Derived Constructor

In the following code:


public class MyClass1
         System.out.println("base class");

14. Anonymous class question

I've a little doubt over this line:

An anonymous class cannot define a constructor
then, why we can also define an Anonymous class with the following syntax:
new class-name ( [ argument-list ...

15. J2SE Question, constructor auto run?

I have wrote C# few years and start to learn java, today i saw a sample is strange ,which is cannot happen in C#.

public class MainClass extends JFrame {


16. Constructor (Java)

I wonder if it's a big error (in small one class Java program) when I define variable in a class level rather that using the constructor? Can ...

17. Constructor Injection, design for testability

I have this code (you probably can ignore that it is Swing code), but I usually end up with too many arguments in my constructor. Should I use model bean ...

18. The constructor Date(...) is deprecated. What does it mean? (Java)

I'm trying to create a Date like this:

date = new Date(year-1900,mon-1,day,hrs,min,sec);
and Eclips gives me this warning: "The constructor Date(int,int,int,int,int) is deprecated". What does it mean for a constructor to be deprecated? What ...

19. Testable Java Code: using model beans with a constructor

According to Misko Hevery that has a testability blog. Developers should avoid 'holder', 'context', and 'kitchen sink' objects (these take all sorts of other objects and are a grab bag ...

20. Constructor Injection using Guice

I have some sample code which is using factories. I'd like to clean up the code by removing the factories and use Guice instead. I attempted to do this but I ...

21. Can I designate a Java-like 'constructor' in c?

I want to 'construct' (read: malloc and memset) my hashtable in c. To do this, I created a function as follows:

int maketable(struct hash_entry **table, int size){

    table ...

22. When to use getInstanceOf instead of constructor

Back couple of months ago I attended a presentation hosted by two representative of an independent software development company. It was mainly about good software design and practices. The two guys were ...

23. Java constructor question

How do I write a constructor to change ints to ints or longs or strings....I am making a Memory system and I have code for Memory and a Memory Element (MemEl) ...

24. Java constructor

How do I define a single constructor public packet(String[] biscuit) which makes my field from private String[] biscuitList to private String[] biscuit?

25. Should Java Have an "is null" construct?

To check against null we generally do if (object == null). Instead, would it be nicer to have

if (object is null) {
   // Do something
if (object is not ...

26. trouble with StringTokenizer

I'm getting the following error message and I can't seem to figure out the problem. Would really appreciate any help. The error message reads as:- cannot find symbol symbol : ...

27. Can a Java class have awareness of its instantiator?

Is there a way for a Java class to have an awareness of its instantiator? For example:

public class Foo() {

    public Foo() {

28. call one constructor from another in java

Hi This was the question asked in interview. Can we call one constructor from another if a class has multiple constructors in java and when?How can I call I mean syntax?

29. What does "this()" do in a constructor?

I have two questions about the following code. 1. How to constructor the third constructor without using setter? 2. what does this() do in the last constructor.

public class Person {


30. Question about Java class constructor

Can somebody tell me what does this mean? I'm going trough Java book and I've encontered this example :

public class Message {


    public Message(String ...

31. Passing "this" in java constructor

Look into the following code:

public class ClassA {
    private boolean ClassAattr = false;

    public ClassA() {    

32. Can someone explain constructors in Java?

I'm learning Java by reading the online Java book, but im finding it hard to understand "constructors". My question is how would I write a constructor that sets private fields of ...

33. Why isn't the "this." command needed in this constructor? (java)

I'm reading a book about java. It just got to explaining how you create a class called "deck" which contains an array of cards as its instance variable(s). Here is the ...

34. How to avoid using this in a constructor

I have this situation:

interface MessageListener
   void onMessageReceipt(Message message);

class MessageReceiver
  MessageListener listener;
  public MessageReceiver(MessageListener listener, other arguments...)
     this.listener = listener;


35. How to call superconstructor in a neat way

So here is my code:

public MyClass (int y) {
    //some code
My problem is that in this case i want to generate a 'x' and ...

36. Designing constructors around type erasure in Java

Yesterday, I was designing a Java class which I wanted to be initalized with Lists of various generic types:

TheClass(List<String> list) {

TheClass(List<OtherType> list) {
This will not ...

37. Getter/Setter (composition, Java, HW)

I have one class called Person that basically looks like:

public class Person
    String firstName;
    String lastName;
    String telephone;
    String ...

38. Why would you have two constructors with the same signature?

What are the use cases of having two constructors with the same signature? Edit: You cannot do that in Java because of which Effective Java says you need static factory. But ...

39. Loading data in constructors and not in constructors

I just want to know the difference between loading the data inside the constructor and loading the data outside the constructor but not inside any methods example: Loading inside constructor

public class ...

40. Doubt based on program in SCJP(EXAM 310-065)

class Top{
public Top(String s){System.out.print("B");}

public class Bottom2 extends Top{
    public Bottom2(String s){System.out.print("D");}
    public static void main(String args[]){
        new Bottom2("C");

41. Doubt based on program in SCJP(EXAM 310-065)

class Building{
        System.out.print("b ");
    Building(String name){

42. constructors in java

Possible Duplicates:
Why do we need a private constructor?
Can a constructor in Java be private?
whts the use of private constructor in java? ...

43. Odd situation for "cannot reference this before supertype constructor has been called"

I'm cannot figure out why this does not compile.

public class A {
    public class B extends A {
        public B(A a) ...

44. Can I set the value of a String in Java without using a constructor?

How-Do/Can I set the value of a String object in Java (without creating a new String object)? Thanks, Chenz

45. Can I create a non-explicit constructor for a Java class?

By default, C++ will do "auto promotion" in assignment if appropriate constructors exist (and are not declared explicit). In Java, this behavior doesn't happen by default. If I want automatic promotion, ...

46. Should we always have a zero-argument constructor in a Class?

Should every Java class have a zero-argument constructor?

47. How can I find out if a string is parseable with jodatimes DateTime constructor?

I need to determine if an input string input can be parsed by jodatimes DateTime constructor Datetime(Object instant) but I'm not interested in creating the DateTime object at this time. Is there ...

48. Constructor SignalStrength() is not visible? What to do?

Yesterday i tried to create an object for this class to be able to use its methods getGsmBitErrorRate() and getGsmSignalStrength(), but Eclipse IDE throws me error that constructor is not visible. ...

49. Are constructors optional in Java or what?

I'm a C# programmer trying to hack at a Java project. Here's an anonymized extract from our production code. It works (I think). Note that this is the whole class.

public class ...

50. Convention in java - "new" oustide of constructor / function?

Simple question. A friend of mind wrote code similar to this one (which is just to explain you my question, it's not useful at all....)

class Example{
    private int[] ...

51. Java cannot find constructor

Like most new programmers I have a small but significant issue that i cannot figure out. My program will not pull my constructor. I have tried quite a few different ways ...

52. constructors (java)

Okay so I have an assignment where I have to create a class with a set of private properties, which I have done. It gets tricky because I'm fairly new to ...

53. How to implement constructor wrapping in Java?

This is what I'm trying to do (in Java 1.6):

public class Foo {
  public Foo() {
    Bar b = new Bar();

54. Will 'this' reference escape from Constructor in this case?

I understand that 'this' reference should not be escaped in Constructor due to thread safety concern, where the object is not yet completely constructed but 'leaked' out to other objects. For ...

55. Which constructor is chosen when passing null?

In the following example, I have 2 constructors: one that takes a String and one that takes a custom object. On this custom object a method "getId()" exists which returns a ...

56. Constructors in Java

Can anybody please tell me what the Constructors are used for exactly in Java? What could be the ideal condition for using the constructors in an application? Thanks, david

57. java constructor function newbie question

Im newbie in Java and im learning it. Right now i have two class, i already called class B on class A constructor

class A
public A {
B bb = new B(textField);

void init() {

58. cannot find symbol - constructor Car()

I'm trying to use a method from another class called Car but referring to it in a class called Bike. I've tried to create an instance variable by using the following ...

59. How do you call a mutator from within a constructor in the same class?

For a homework assignment the instructions state (within Undergrad class): You do NOT need to include a default constructor, but you must write a full parameterized constructor (it takes 4 arguments) -- ...

60. Question about constructors in Java

I have few questions regarding Java constructors

  1. Can a constructor be private? If yes then in which condition?
  2. Is a constructor a method or not?
  3. If a constructor does not return anything then why ...

61. Replace constructor with a factory/or a builder

I am using IntelliJ 10 Comnunity Edition, and I noticed there are two refactoring options which are similar: -Replace constructor with factory -Replace constructor with builder What are the differences between these two? When ...

62. Java "this" in constructors

Well, this is a very basic question, I've never coded in java, but I'm writing a class for a friend... Having something like:

class myClass{

    private string ...

63. String constructor with null value

why String (String) constructor with null value cause compile-time error? I think there is 2+ constructor that takes Object and when init. it with null it doesn't know which to start. ...

64. java constructor best practice

What is the advantage of having constructor simillar to the one mentioned below:-

class A{
public A(A a){}
public A(){}

65. A design pattern for constructors

I have been challenged by a design issue which I will try to describe below. Suppose that a class, call it A, has a constructor with a bunch of parameters. Since ...

66. where should I create a constructor and where should i not?

I'm beginner in Java language , should I create a constructor method for every class ?!! and for example

public class Cube2 {

    int length;
    int breadth;

67. Is this the way Constructor in Java allocates memory?

Default constructor is automatically called after an object is created. But in Java when we allocate memory using new operator i.e. classname obj = new classname(); the constructor is automatically invoked ...

68. What's wrong with this? Cannot find symbol. symbol - constructor

public MyLine(double x, double y)

   MyLine p1 = new MyLine();

   p1.x = x;

   p1.y = y;

That's my code and the error I get is
./ cannot find ...

69. Can we stop the run of a constructor?

I need to create an object of some type. The class of the object has just one constructor (one that I've written). My program receive requests to create instances of an objects ...

70. Is too many params in a constructor for a factory a code smell?

I have a factory class that currently takes 6 params in it's constructor, and I just hit a need to add another. Normally, this would scream to me "Hey, your class has ...

71. How can a Java class have no no-arg constructor?

The Oracle Java tutorial site has this paragraph that is confusing me:

All classes have at least one constructor. If a class does not explicitly declare any, the ...

72. Java constructors for side-effects only

I have a Java instance class, "ResultMaker" that exists for side-effects only (sending an email) and the object is never subsequently used. (Of course this could be re-written so that ...

73. Getting value from constructor in another class

I am sure this is a very easy question for many, but I am struggling with it. I am trying to get a value from the following constructor and place ...

74. at what point in time does this.getServletName() begin to work and what is the rationale

I find that this.getServletName() fails in a constructor but works in a method. Note getServletName() is provided by the parent of the parent. This was observed in Google App ...

75. Java - cannot find symbol - constructor

I'm trying to use a method from another class called Digits but referring to it in a class called FourDigits. I've tried to create an instance variable by using the following ...

76. Java-Constructors of Classes

I have this class: When I'm trying to define a new Instense:

Point nir= new Point(double x, double y);
I'm, getting the error: Multiple markers at this line - x cannot be ...

77. if else condition in class constructor ... is it good practice?

I have written a constructor and passing one boolean flag to decide which value to set to class variable. Code is as follows

public PDFParagraph(PDFPhrase phrase,boolean isRtl) {

78. Is there any Virtual Constructor in Java?

is there any term call Virtual Constructor in Java?then where we need to use this?

79. Think about Java constructor

In this example:

class A {
    public A() {
        // pre-init1
        // post-init1

80. Java Constructor help

// A bank account class with methods to deposit to, withdraw from,
// change the name on, and get a String representation
// of the account.
import java.util.Random;
public class Account
  private double ...

81. Which new is execute first -- in constructor or out?

If I define a class like following:

public class myClass {
    private x = new anotherClass();
    private y;

    public myClass() {

82. Java consructor without name?

When I run the below code I am getting output as:

static block
TEst block
main block
How does the string "TEst block" gets printed? Is it considered as constructor?
public class TestBlk {

static {

83. using an attribute of a class that has been initialised in a constructor

If I set a value of an attribute of a class and use final, do i have to initialise the attribute as a parameter of the class constructor? For ...

84. PDFJET Does Not Work For En Empty Constructor

i want to use pdfjet for a Google app engine project. i downloaded the Java jar from the pPdfjet home page. i followed an example given in a stack-overflow example and the examples ...

85. java enum with enum in constructor

Is it possible to let a enum in java take a set of enums as as argument? If yes, then how do I implement it? When using this I whant to be ...

86. I removed a necessary constructor, yet it still compiles and runs

Whilst tidying up my project by removing what I believed to be unnecessary code, I removed a constructor of the form

public MyClass(int a,  int b) 
leaving in place the ...

87. What is the purpose of mixed constructors?

What is the purpose of doing something like:

Employee a = new OverTimeEmployee();
OverTimeEmployee a = new Employee();
Where OverTimeEmployee is a subclass of employee? and what is the proper name for it? I ...

88. Java constructors

Possible Duplicate:
About Constructors in Java
Can a constructor in java throw exceptions? What all things we need to keep in mind about this when it comes ...

89. Force GSON to use specific constructor

public class UserAction {
    private final UUID uuid;
    private String userId;
    /* more fields, setters and getters here */


90. Pretty simple constructor question that I just can't get. Java

  • Create a class with a default constructor (one that takes no arguments) that prints a message. In your main() method, create an object of this class.
  • Add an overloaded constructor to your ...

91. EnumMap constructor not found

Given that I have the requisite

import java.awt.Color;
import java.util.EnumMap;
enum Terrain { ... }
then as far as I can tell from the documentation, this should work
static EnumMap<Terrain, Color> colors = new EnumMap<Terrain, Color>(Terrain.class);
but ...

92. Add constructor to deftype created class

For the purposes of interoperability with Java, I need a class that has a nullary constructor that performs initialization. Objects of this class need to have something resembling mutable java fields (namely, ...

93. How to initialise BigInteger after creating instants(constructor can't be called)

Imagine an instance of BigInteger, then how to initialize it after creating instance? For example:

BigInteger t = new BigInteger();
How to put a value in t? If the constructor cannot be called, then what ...

94. Java Architecture - should commonly used classes be passed around in constructors?

I'm designing a GUI desktop app in Java, which has a tabbed interface (like the tabs in your browser). The MainWindow class creates the tabbed window, loading other SWT classes that have ...

95. Java - Date constructor accepts a Date String, But deprecated. Tried alternatives, but no luck

String temp_date="07/28/2011 11:06:37 AM";  
    Date date = new Date(temp_date); //Depricated 
    SimpleDateFormat sdf = new SimpleDateFormat("MMM-dd-yyyy hh:mm:ss"); 
    String comp_date= ...

96. Need to know order in which the constructors are called in the program

I need to know the order, in which the constructors will be called. Point class:

public class Point
    public int x = 0;
    public int y = ...

97. What's wrong with the Java Date constructor Date(long date)?

I have two objects, p4 and p5, that have a Date property. At some points, the constructor works fine:

p4.setClickDate(new Date(System.currentTimeMillis() - 86400000 * 4));
Sets the date to Sun Jul 31 ...

98. cannot find symbol - constructor in Java

i get the cannot find symbol - constructor Occupant(Position) when i try to compile the sub class Animal of Occupant

public class Occupant
protected Position position;
public String string=" ";
protected String name;
protected String description;

public Occupant(Position ...

99. class constructor cannot be accessed by outside package

so i can't find a question already asked that answers my exact problem. I have a package that i wrote in eclipse that i exported as a jar library to use ...

100. why does Joda Time allow a Period constructor to take two LocalTimes but there is no Duration constructor like that?

Why does Joda Time allow a Period constructor to take two LocalTimes but there is no Duration constructor like that? I want to know because it may aid in my understanding of ...  | Contact Us | Privacy Policy
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