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Editor to share with you what is the difference between = = and equals () in Java. I hope you will get something after reading this article. Let's discuss it together.

1. =

= = is the operator used to determine whether two values are equal, and can be used in basic data type variables and reference data type variables

1.1 basic data types

There are eight basic data types of Java, which can be divided into three categories.

Character type char

Boolean type boolean

Numeric types byte, short, int, long, float, double

There is an exception here. Boolean does not participate in numerical operations.

Int A1 = 10 int a2 = 10 System.out.println (true); / / System.out.println (true); / / System.out.println (System.out.println); / / System.out.println (a3==a4); / / System.out.println (System.out.println); / / System.out.println (a3==a4); / / System.out.println (a3==a4); /

The above gives several sets of examples, the same data types can be compared with each other, needless to say, what about different data types?

Int A1 = 10 byte b1 = 10 system. Out.println (a1==d1); / / trueint A1 = 'alternate switch int c2 = 65 system. Out.println (C1 = = c2); / / true A1 = 10 double D1 = 10.0dscape System.out.println (a1==d1); / / true A1 = 10 mitchar e1 = 10 System.out.println (a1==e1); /

As you can see, within the scope of basic data types, different data types can also be compared directly.

If you are comparing the basic data types, you are judging whether the two saved data are the same (not necessarily of the same type).

1.2 reference data type

Here we first write a Student class for reference

Public class Student {public String name; public int age; public Student () {} public Student (String name, int age) {this.name = name; this.age = age;}}

Instantiate two Student objects to determine whether they are equal or not

Student student1= new Student ("Tom", 18); Student student2 = new Student ("Tom", 18); System.out.println (student1==student2); / / false

Notice that the first false in the example appears here. As you can see, even if the value assigned is the same, the result judged with = = is false, because the two objects do not point to the same address in memory.

If you are comparing reference types, you are comparing whether two variables represent the same object entity, that is, whether they point to the same address.

1.3 Summary

= = is the operator

Can be used in basic data type variables and reference data type variables

If you are comparing the basic data types, you are judging whether the two saved data are the same, not necessarily the same type.

If you are comparing reference types, you are comparing whether two variables represent the same object entity, that is, whether they point to the same address.

2. Equals

Equals () is a method and can only be used to reference data types

Or do you use the Student object described above, if you use equals comparison, then?

Student student1 = new Student ("Tom", 18); Student student2 = new Student ("Tom", 18); System.out.println (student1.equals (student2)); / / false

The answer is still false. We can take a look at the source code of equals used here.

It is the equals () method in Object (inheritance) that is used, while the equals () method in Object also uses = = for comparison

Equals () and = = have the same effect in the Object class

Ah, some students may want to say that this equals () is not quite the same as what we usually use, ah, the equals () usually used seems to be used to compare numerical values. Here we take the String class as an example.

String str1= new String ("cun"); String str2 = new String ("cun"); System.out.println (str1==str2); / / falseSystem.out.println (str1.equals (str2)); / / true

Use = = to compare, not surprisingly, false. Using equals () here, the result is true. Let's take a look at the equals () source code (Java8 version) here.

As you can see, equals () in the String class overrides equals () in the Object class, which focuses on specific numerical comparisons (we also prefer more specific values in our daily use). Analyze the source code, here first use = = to compare, then determine whether it is an example of String, determine whether the length is equal, and finally determine whether the characters are equal one by one.

Most of the source code programs are easy to understand, and some people are confused about the cast here (as shown in the figure below). Since the previous sentence determines whether it is an instance of the String class, why does the latter sentence have to be forcefully changed? This is because, in Java, the code from writing to execution has to go through two processes-compilation and execution, during execution, the program determines whether the argument is an instance object of the String class, and then there is no need for a strong turn; but in compilation, even after the instanceof judgment, the compiler will always treat the passed parameters as the Object type, while the Object type has no value attribute and will report an error directly. So if you don't force it here, the compiler won't pass, let alone execute it.

Similarly, we can write the equals () method overridden in the Student class.

But now because classes are used a lot, on the one hand, it is cumbersome to add each class, on the other hand, we may not write robust enough. Here are two ways to automatically provide rewriting of equals ().

The shortcut key for the IDEA compiler, "alt + insert", select the options shown in the following figure

Select the attributes that need to be added to equals ()

You can see the automatically generated program

Overridepublic boolean equals (Object o) {if (this = = o) return true; if (o = = null | | getClass ()! = o.getClass ()) return false; Student student = (Student) o; return age = = student.age & & Objects.equals (name, student.name);}

Import lombok package and add Data comments

@ Datapublic class Student {public String name; public int age; public Student () {} public Student (String name, int age) {this.name = name; this.age = age;}}

You can see that the equals () method in the Object class has been overridden

3. Summary / * * = = is the operator, equals is the method * 1. = = * can be used in basic data type variables and reference data type variables * if you are comparing basic data types, you can judge whether the two saved data are the same, not necessarily the same type * if you are comparing reference types Is to compare whether two variables represent the same object entity, that is, whether they point to the same address * * 2. Equals * can only be used for reference data types * equals () and = = have the same function in the Object class * equals in the String, Data, File, wrapper classes, etc., all overrides the equals () method in the Object class. The comparison is whether the physical content is the same * / after reading this article, I believe you have a certain understanding of "what is the difference between Java = and equals ()". If you want to know more about it, welcome to follow the industry information channel, thank you for reading!

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