[ACCEPTED]-call one constructor from another in java-constructor
You can, and the syntax I know is
this(< argument list >);
You can 5 also call a super class' constructor through 4
super(< argument list >);
Both such calls can only be done as the 3 first statement in the constructor (so you 2 can only call one other constructor, and 1 before anything else is done).
Yes, you can do that.
Have a look at the 2 ArrayList implementation for example:
public ArrayList(int initialCapacity) {
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity];
}
/**
* Constructs an empty list with an initial capacity of ten.
*/
public ArrayList() {
this(10);
}
The second constructor 1 calls the first one with a default capacity of ten.
None of the answers are complete, so I'm 5 adding this one to fill in the blanks.
You 4 can call one constructor from another in 3 the same class, or call the super class, with 2 the following restrictions:
- It has to be the first line of code in the calling constructor.
- It cannot have any explicit or implicit reference to
this. So you cannot pass an inner class (even an anonymous one if it references any instance methods), or the result of a non-static method call, as a parameter.
The syntax (as 1 mentioned by others) is:
MyClass() {
someInitialization();
}
MyClass(String s) {
this();
doSomethingWithS(s);
}
FYI, this is called the telescoping/telescopic constructor pattern.
It's discussed 1 in JLS 8.8.7.1 Explicit Constructor Invokations
- Alternate constructor invocations begin with the keyword
this(possibly prefaced with explicit type arguments). They are used to invoke an alternate constructor of the same class.- Superclass constructor invocations begin with either the keyword
super(possibly prefaced with explicit type arguments) or a Primary expression. They are used to invoke a constructor of the direct superclass.
this(other, args);
0
example:
public class FileDb {
/**
*
*/
public FileDb() {
this(null);
}
public FileDb(String filename) {
// ...
}
}
0
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