Attempt to override equals() & hashCode() - please point out error(s)!

The hashCode() method is based on a Whizlabs example, the rest is not.
Neither equals nor hashCode appear to be overriding the java.lang.object methods, and I do not know why. The signature is the same.

The output is this, which shows that the default methods are still being used?

package collections_whizExam;

public class Q64_hashCode_intArray {
	public Integer[] arr1 = {1,2,3,4,5};
	public Integer[] arr2 = {1,2,3,4,5};
	public Integer[] arr3 = {3,3,3,3,3};
	public Integer[] arr4 = {2,3,4,5,6};
	
	public boolean equals(Object o){
		boolean b = false;
		if(o instanceof Integer[]){
			if(((Integer[]) o).length==5){
				Integer sum=0; 
				Integer[] test = ((Integer[]) o);
				for(Integer s : test)sum+= s; 
				if(sum==15) b=true;
			}
		}
		return b;	
	}

public int hashCode(Object o){
		int hash = 7;
		Integer myArray[];
		if(o instanceof Integer[]){
			myArray = ((Integer[]) o);
			if(myArray == null)
				hash = 31 * hash + 0;
			else
				for(int i=0; i<myArray.length; i++)
				{hash = 31 * hash +(myArray[i] == null? 0 : myArray[i]);}
		}
			return hash;
	}
	
	public static void main(String[] args) {
		Q64_hashCode_intArray q64 = new Q64_hashCode_intArray();
		System.out.println("arr1 equals arr2?:\t\t\t" + q64.arr1.equals(q64.arr2));
		System.out.println("q64.arr1.hashCode():\t\t\t" + q64.arr1.hashCode());
		System.out.println("System.identityHashCode(q64.arr1):\t" + System.identityHashCode(q64.arr1));
		System.out.println("q64.arr2.hashCode():\t\t\t" + q64.arr2.hashCode());
		System.out.println("System.identityHashCode(q64.arr2):\t" + System.identityHashCode(q64.arr2));
	}
}

Constructive comments only please. Thank you.

Nigel Shrin wrote:The hashCode() method is based on a Whizlabs example, the rest is not.
Neither equals nor hashCode appear to be overriding the java.lang.object methods, and I do not know why. The signature is the same.

No - hashCode(Object) is different from hashCode(). You're not overriding unless the number and types of the parameters are the same. One has no parameters, while the other has a single Object parameter. Not the same.

And your overriden equals method expects an object of type 'Q64_hashCode_intArray' (not Integer[]).

This is my first attempt at creating my own equals() & hashCode(); it is closer but still not quite right, I realised I need to pass an object and cannot use it to compare arrays within an object.
This is closer, but the last two lines return (equals) TRUE when they should be FALSE, can someone highlight my error please?

public class Q64b {
	
	public Integer[] arr1 = new Integer[5];

Q64b(Integer[] arr){
		this.arr1=arr;
	}
		
	public boolean equals(Object o){
		boolean b = false; Integer sum=0; 
		if(this.arr1.length==5){
			for(Integer s : this.arr1){
				sum+= s; 
				if(sum==15){
					b=true;
				}
			}
		}
		return b;	
	}

public int hashCode(){
		int hash = 7;
		if(this.arr1 instanceof Integer[]){
			if(this.arr1 == null) hash = 31 * hash + 0;
			else{
				for(int i=0; i<this.arr1.length; i++)	{
					hash = 31 * hash +(this.arr1[i] == null? 0 : this.arr1[i]);
				}
			}
		}
			return hash;
	}
	
	public static void main(String[] args) {
		
		Integer[] a1 ={1,2,3,4,5};
		Q64b instance1 = new Q64b(a1);
		System.out.format("%1$-40s %2$15d \n","instance1 Nigel's hashCode value is:", instance1.hashCode());
		System.out.format("%1$-40s %2$15d \n\n","System.identityHashCode(instance1) is:", System.identityHashCode(instance1));
		
		Integer[] a2 ={1,2,3,4,5};
		Q64b instance2 = new Q64b(a2);
		System.out.format("%1$-40s %2$15d \n","instance2 Nigel's hashCode value is:", instance2.hashCode());
		System.out.format("%1$-40s %2$15d \n\n","System.identityHashCode(instance2) is:", System.identityHashCode(instance2));
		
		System.out.format("%1$-40s %2$15b \n\n", "instance1 equals instance2? is:", instance1.equals(instance2));	
		
		Integer[] a3 ={2,3,4,5,6,7,8};
		Q64b instance3 = new Q64b(a3);
		System.out.format("%1$-40s %2$15d \n","instance3 Nigel's hashCode value is:", instance3.hashCode());
		System.out.format("%1$-40s %2$15d \n\n","System.identityHashCode(instance3) is:", System.identityHashCode(instance3));
		
		System.out.format("%1$-40s %2$15b \n", "instance1 equals instance3? is:", instance1.equals(instance3));	
		System.out.format("%1$-40s %2$15b \n\n", "instance2 equals instance3? is:", instance2.equals(instance3));	
	}
}

thank you very much

You might also want to check out #28 in the JavaBeginnersFaq.

What is this used for ?

What is this used for ?
if(this.arr1.length==5){

I wanted to say this object is equals if the array has five elements and their sum comes to 15, just as an experiment in learning to use equals() and hashCode(). The array is obviously is declared as 5, but it could be a stringBuffer etc. It has no purpose beyond trying to understand the implementation.

Ulf Dittmer wrote:You might also want to check out #28 in the JavaBeginnersFaq.

Hi Ulf,
thanks for the links, I bought the Effective Java book after reading them.