Java only has value passing! Why?

Irving the procedural ape 2020-11-07 22:18:21
java value passing


From the public number : Program control

A basic question for an interviewer to ask :Java Value passing or reference passing ?

Everyone must have their own views on this issue , So what the truth is , How can we answer the interviewer's question ? Today, let's analyze a wave of

Value passed ? reference ?

First , We need to know what Value passed , What do you mean reference , Know this to understand Java How to do it . To understand these two kinds of transmission, we need to understand the concept of formal parameter and actual parameter

Formal parameters : The parameters used when defining a function , Used to receive function input parameters , For example, let's write a function , The parameters in the function are formal parameters

(String str) { System..println(str)}

The actual parameter : When we call a function , The arguments in parentheses after the function name are called actual arguments , As shown in the following example

(String[] args) { A a = A()a.test()}

You can find , When you call a function with parameters , The actual parameters are passed to the formal parameters ; So there are two situations in the process of transmission , namely Value passing and reference passing

Value passing is to give you the value of the parameter , When the function is called, a copy of the actual parameter is passed into the function , In this way, the modification of parameters inside the function will not affect the actual parameters ; And reference passing is different , It directly gives the actual address of the parameter to the calling function , The content of the address can be modified directly inside the function , Will affect the actual parameters

Let me give you an example , We have a database A, Only internal personnel are allowed to operate , Now there's a project to work with other companies , The data of this database needs to be handed over to the partner company , I can't put my database directly A Give them the address , Let them connect directly to our database A Well , If they delete the library and run away , Then I boss Don't you want to sacrifice me to heaven

So at this point , Copy our database table data to a new database B, Partners can look at this database B data , They can also operate at will , It will not affect our database

This operation is similar to value passing , If the cooperative company directly operates our database , It's like reference passing , Now we should know the difference between the two

Java Value passing or reference passing ?

We learned about the concepts of value passing and reference passing , that Java What kind of transmission is it in China ? Let's look at code analysis

(String[] args) { Fans fans = Fans()t = fans.test(t)System..println(+ t) }
(t) { t = System..println(+ t) }
// Output In testIn main

The above code , stay main In the definition of t The value of is 1, In function test Parameters have been modified in t The value of is 2, Is this result easy to analyze ?test The function does not change the incoming t Value , Then according to our introduction above, can we draw a conclusion :Java Value passing in

Some people may question , The parameters you pass in t Is the basic type , If you pass in a reference object type , That would change the content of the object ,OK, Let's look at a reference type code

= String = (Fans fans) { fans.= fans.= System..println(+ fans.++fans.)}
(String[] args) { Fans fa = Fans()fa.test(fa)System..println(+ fans.getA()++fans.getB())}
// Output 
In testABnewFansIn mainABnewFans

Ah , The output turns out to be the same , That is, the incoming fans Objects are functions test Revised , So is it a reference passing again ?

So I came to the conclusion that , The basic type is value passing .........

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