hashcode and equals in java

For the characteristics of the equals of the object class, for non-null references:1. Reflexivity: X.equals (x) return true;2. Symmetry: X.equals (y) is true, then y.equals (x) is also true;3. Transitivity: X.equals (y) is true,y.equals (z) is true, then X.equals (z) is also true;4. Consistency: X.equals (y) is the first call to True, then X.equals (y) for the second time, third time, ... , the nth invocation is also true, provided that no x is modifi

, whether the values in memory for the two variables are equal (whether they point to the same storage space), you can compare them with the "= =" operator. However, if you want to compare the contents of these two objects to be equal, then the "= =" operator cannot be implemented. 2 equals is one of the methods provided by the object class. Each Java class is integrated from the object class, so each obje

);}} In hashmap, get () is used to obtain the value, put () is used to insert the value, and containskey () is used to check whether the object already exists. It can be seen that, compared with the arraylist operation, hashmap not only indexes its content through the key, but also has little difference in other aspects. As mentioned above, hashmap is based on hashcode. There is a hashcode () method

If you write the equals method for a class, you should write the hashcode method at the same time.If the hashcode method is not provided, the compiler does not report errors and may not encounter any problems.Conflict-based hash tables (similar to Java. util. Set also use the same hash table) may cause unpredictable co

hashcode values must be the same; 2. If the hashcode of the two objects is the same, they are not necessarily the same (that is, false is returned for comparison with equals) Self-understanding: the hashcode method is implemented to improve program efficiency, and the comparison of

From the beginning of learning Java, from each senior, all kinds of books, the major sites to hear, see, rewrite the Equals method must override the Hashcode method. Overriding the Equals method must override the Hashcode method. Overriding the

Java Collection-hashCode, java-hashcodeRole of hashCode There are two types in the Java Set: List and Set. The difference between them is that the element division in the List Set is ordered and can be repeated, elements in the Set are unordered and cannot be duplicated. The

classes that do not override the two methods. string equals () The same is true if the memory address is the same and the content is the same.The storage address is different to satisfy the length, the hash code, the corresponding characters are the same to return true. hashcode of String () @Override public int hashcode () { int hash =

First, let's talk about the recommended situation: for example, when your object wants to be put into a set or a map key (non-Hash set and map, such as treeset and treemap ), then you must override the equals () method to ensure uniqueness. Of course, in this case, you do not want to rewrite the hashcode () method, and there is no error. However, for a good programming style, you should rewrite the

Hashcode method, the first hashcode comparison, if different, that does not need to be in the comparison of equals, so significantly reduce the equals comparison The number of times, this contrast needs to compare the number of significant efficiency improvement is very obvious, a good example is the use of the set;

We all know that the Java language is fully object-oriented, and in Java, all objects are inherited from the object class.The Equals method compares the addresses of two objects to the address, Hashcode is a local method, and returns the object address value. There are two methods