Equals increases execution speed / performance optimization

In principle, it is close to bron filter .
When you add objects to HashSet when ,HashSet Meeting First calculate the value of the object hashcode value To determine where objects are added , At the same time With other objects that have been added to this location hashcode Comparison of values , If No match Of hashcode,HashSet Meeting Assume that the object does not recur . But if you find It's the same hashcode value The object of , And then it will call equals() Methods to check hashcode Are equal objects really the same . If The two are the same ,HashSet It won't make the join operation successful . If it's different , It will be re hashed to other locations .

public class test1 {
    
	public static void main(String[] args) {
    
		String a = new String("ab"); // a  For a quote 
		String b = new String("ab"); // b For another reference , Object has the same content 
		String aa = "ab"; //  Put in constant pool 
		String bb = "ab"; //  Find from constant pool 
		if (aa == bb) // true
		System.out.println("aa==bb");
		if (a == b) // false, Not the same object 
		System.out.println("a==b");
		if (a.equals(b)) // true
		System.out.println("aEQb");
		if (42 == 42.0) // true
		System.out.println("true");
	}
}

This greatly reduces equals The number of times , Accordingly, the execution speed is greatly improved . We can see from it that ： hashCode() Its function is to get hash code , Also known as hash code ; It actually returns a int Integers . The function of this hash code is to determine the index position of the object in the hash table .hashCode() Only useful in hash tables , In other cases it doesn't work . In the hash table hashCode() Is used to get the hash code of an object , Then determine the position of the object in the hash table .