This is an example of how to initialize a constructor with composition. We have created an object with reference to another object, as described below:
- We have created class
Athat has a String field and overrides thetoString()API method of Object, where it returns its String field. - We have also created a class,
Compositionthat has four String fields, a field that is reference toA, an int field and a float field. Compositionclass has a constructor using its fields and also overrides thetoString()API method of Object.- We create a new instance of
Compositionand call itstoString()method to print it. - Its constructor is called where
Aconstructor is also called to initializeAfield. - Then its
toString()method is called, that returns all values of Composition’s fields.
Let’s take a look at the code snippet that follows:
package com.javacodegeeks.snippets.core;
class A {
private String s;
A() {
System.out.println("A()");
s = "Constructed";
}
@Override
public String toString() {
return s;
}
}
public class Composition {
private String string1 = "Happy", string2 = "Happy", string3, string4;
private A obj;
private int i;
private float toy;
public static void main(String[] args) {
Composition b = new Composition();
System.out.println(b);
}
public Composition() {
System.out.println("Inside A()");
string3 = "Joy";
i = 47;
toy = 3.14f;
obj = new A();
}
@Override
public String toString() {
if (string4 == null) // Delayed initialization:
{
string4 = "Joy";
}
return "s1 = " + string1 + "n" + "s2 = " + string2 + "n" + "s3 = " + string3 + "n"
+ "s4 = " + string4 + "n" + "i = " + i + "n" + "toy = " + toy
+ "n" + "castille = " + obj;
}
}
Output:
Inside A()
A()
s1 = Happy
s2 = Happy
s3 = Joy
s4 = Joy
i = 47
toy = 3.14
castille = Constructed
This was an example of how to initialize a constructor with composition in Java.
