Java judges whether two objects are equal. Springboot is a medium-sized project

System.out.println(“a==b”);

if (a.equals(b)) // true

System.out.println(“aEQb”);

if (42 == 42.0) { // true

System.out.println(“true”);

}

}

}

explain ：

• String Class equals The method is rewritten , therefore String Of equals The method compares the value of the object , and Object Of equals Method is to compare the memory address of the object ;

• When creating a String When an object of type , The virtual machine looks in the constant pool for objects that have the same existing value as the value to be created , If so, assign it to the current reference . If not, recreate one in the constant pool String object .

 2 Use hashCode And equals Judge

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hashCode Is used to get the hash code , It can also be called hash code , The actual return value is one int Type data , It is often used to determine the position of an object in a hash table .

Because superclass Object There is hashcode Method , This means that all classes have hashCode Method .

Example ： By rewriting equal Method , Make the contents of two objects the same , Then the hash codes of the two objects are different .

public class EqualTest {

public static void main(String[] args) {

Person p1 = new Person(10, “ Zhang San ”);

Person p2 = new Person(10, “ Zhang San ”);

System.out.println(

“p1.equals(p2)=” + p1.equals(p2) + “, p1.hashcode=” + p1.hashCode() + “, p2.hashcode=” +p2.hashCode());

}

}

class Person {

int age;

String name;

……

@Override

public boolean equals(Object obj) {

if (this == obj) return true;

if (obj == null) return false;

if (getClass() != obj.getClass()) return false;

Person other = (Person) obj;

if (age != other.age) return false;

if (name == null) {

if (other.name != null)

return false;

} else if (!name.equals(other.name)){

return false;

}else{

return true;

}

}

}

Because there is no rewriting hashCode Method , So the output is ：

Last , Attach a brain map prepared before the interview ：

Before the interview, you must brush the questions , In order to facilitate everybody to review , I'd like to share a collection of personal interviews

• Java Organize the core knowledge

• Spring Family bucket （ Practical series ）

Step3： Brush problem

Since it's an interview , Then it's necessary to brush the questions , In fact, after the Spring Festival home , I can't go anywhere , I did a lot of interview questions myself , So in the interview process to be able to know , Basically, it will be clear what knowledge points will be asked during the interview , What are the high frequency questions , So brushing questions is a very important point in the pre interview preparation process .

The following is my private interview question bank ：

Many people sigh “ Learning is useless ”, In fact, the reason why there is the theory of uselessness , It's because what you want doesn't match what you learn , This means that I have not learned enough . Whether it's study or work , There should be initiative , So if you have a big factory dream , Then we should try our best to realize it .

Finally, I wish you all good health , I got what I wanted offer！

This article has been  CODING Open source project ：【 A big factory Java Analysis of interview questions + Core summary learning notes + The latest explanation video + Actual project source code 】 Included