public
<T> T[] toArray(T[] a)
Returns
an array containing all of the elements in this set; the run time
type of the returned array is that of the specified array.
import java.util.*; class TreeSetCopyToSpecificArray{ public static void main(String args[]){ TreeSet<Double> mySet = new TreeSet<> (); Double myArray[]; int size; /* Add Elements to the Set */ mySet.add(55.6); mySet.add(10.01); mySet.add(5.01); mySet.add(-100.123); /* Get the size of the Set*/ size = mySet.size(); /* Initialize the size of myArray */ myArray = new Double[size]; /* Copy Elements to the myArray of type Double*/ mySet.toArray(myArray); /* Display the elements of the Array */ System.out.println("Elements in the Array are"); for(Double obj : myArray) System.out.println(obj); } }
Output
Elements in the Array are -100.123 5.01 10.01 55.6
1. If
the set fits in the specified array, it is returned, Otherwise, a
new array is allocated with the run time type of the specified array
and the size of this set.
import java.util.*; class TreeSetCopyToSpecificArray{ public static void main(String args[]){ TreeSet<Double> mySet = new TreeSet<> (); Double myArrayParam[] = new Double[2]; Double myArrayReturn[]; int size; /* Add Elements to the Set */ mySet.add(55.6); mySet.add(10.01); mySet.add(5.01); mySet.add(-100.123); /* Copy Elements to the myArray of type Double*/ myArrayReturn = mySet.toArray(myArrayParam); /* Display the elements of the Array */ System.out.println("Elements in the myArrayParam are"); for(Double obj : myArrayParam) System.out.println(obj); System.out.println("\nElements in the myArrayReturn are"); for(Double obj : myArrayReturn) System.out.println(obj); } }
Output
Elements in the myArrayParam are null null Elements in the myArrayReturn are -100.123 5.01 10.01 55.6
As
you observe the output, the size of the Array myArrayParam is 2,
which is less that the set size 4. So the elements in the set are not
copied to the Array myArrayParam.
If
the myArrayParam has the size 4, exactly as the set size, then the
elements are copied to myArrayParam and at the same time to the Array
myArrayReturn also.
import java.util.*; class TreeSetCopyToSpecificArray{ public static void main(String args[]){ TreeSet<Double> mySet = new TreeSet<> (); Double myArrayParam[] = new Double[4]; Double myArrayReturn[]; int size; /* Add Elements to the Set */ mySet.add(55.6); mySet.add(10.01); mySet.add(5.01); mySet.add(-100.123); /* Copy Elements to the myArray of type Double*/ myArrayReturn = mySet.toArray(myArrayParam); /* Display the elements of the Array */ System.out.println("Elements in the myArrayParam are"); for(Double obj : myArrayParam) System.out.println(obj); System.out.println("\nElements in the myArrayReturn are"); for(Double obj : myArrayReturn) System.out.println(obj); } }
Output
Elements in the myArrayParam are -100.123 5.01 10.01 55.6 Elements in the myArrayReturn are -100.123 5.01 10.01 55.6
1. If
the Array size is greater than the set size, then the element in the
array immediately following the end of the set is set to null.
import java.util.*; class TreeSetCopyToSpecificArray{ public static void main(String args[]){ TreeSet<Double> mySet = new TreeSet<> (); Double myArrayParam[] = new Double[10]; Double myArrayReturn[] = new Double[10]; int size; /* Add Elements to the Set */ mySet.add(55.6); mySet.add(10.01); mySet.add(5.01); mySet.add(-100.123); /* Copy Elements to the myArray of type Double*/ myArrayReturn = mySet.toArray(myArrayParam); /* Display the elements of the Array */ System.out.println("Elements in the myArrayParam are"); for(Double obj : myArrayParam) System.out.println(obj); System.out.println("\nElements in the myArrayReturn are"); for(Double obj : myArrayReturn) System.out.println(obj); } }
Output
Elements in the myArrayParam are -100.123 5.01 10.01 55.6 null null null null null null Elements in the myArrayReturn are -100.123 5.01 10.01 55.6 null null null null null null
2. toArray
method throws NullPointerException if the specified Array is null
import java.util.*; class TreeSetCopyToSpecificArray{ public static void main(String args[]){ TreeSet<Double> mySet = new TreeSet<> (); Double myArrayParam[]; myArrayParam = null; /* Add Elements to the Set */ mySet.add(55.6); mySet.add(10.01); mySet.add(5.01); mySet.add(-100.123); /* Copy Elements to the myArray of type Double*/ mySet.toArray(myArrayParam); /* Display the elements of the Array */ System.out.println("Elements in the myArrayParam are"); for(Double obj : myArrayParam) System.out.println(obj); } }
Output
Exception in thread "main" java.lang.NullPointerException at java.util.AbstractCollection.toArray(AbstractCollection.java:176) at TreeSetCopyToSpecificArray.main(TreeSetCopyToSpecificArray.java:15)
3. toArray
throws ArrayStoreException if the runtime type of the specified
array is not a supertype of the runtime type of every element in
this set.
import java.util.*; class TreeSetCopyToSpecificArray{ public static void main(String args[]){ TreeSet<Double> mySet = new TreeSet<> (); Integer myArrayParam[] = new Integer[10]; /* Add Elements to the Set */ mySet.add(55.6); mySet.add(10.01); /* Copy Elements to the myArray of type Double*/ mySet.toArray(myArrayParam); } }
Output
Exception in thread "main" java.lang.ArrayStoreException: java.lang.Double at java.util.AbstractCollection.toArray(AbstractCollection.java:188) at TreeSetCopyToSpecificArray.main(TreeSetCopyToSpecificArray.java:12)
Set
is of type Double, but the Array which is passes to the toArray
method is of type Integer, which is not a sub class of Double, So
ArrayStoreException thrown.
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