brief introduction

Kotlin has developed rapidly recently, making many Java developers turn to Kotlin. How do the two languages compare?

Advantages of Kotlin

1. Simplify handling of null objects (prevent null pointers)

val userName = a?.b?.c?.d ?: ""

2. Attribute access, instead of Get/Set method

Kotlin code

class User {
    var name :String?=null
}

java code

public class User {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

See why the Kotlin property access method is better than Java's Get/Set method to learn more

3. Default constructor

Kotlin code

class User(var name: String)

java code

public class User {

    private String name;

    public User(String name) {
        this.name = name;
    }

    public String getName() {
        return name.toUpperCase();
    }

    public void setName(String name) {
        this.name = name.toUpperCase();
    }
}

4. Simplify object property calls (using with, apply, let, etc.)

Kotlin code (to avoid repeating the name of the object)

val user = User()
with(user)
{
    name = "jerry"
    age = 18
}

java code

User user = new User();
user.setName("jerry");
user.setAge(18);

5. Android automatically binds the control definition in the xml file

It is no longer necessary to use findViewById or ButterKnife, use the sample:

import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        .....
        textView.text = "hello"
    }
}

6. Simplify Parcelable implementation

import android.os.Parcelable
import kotlinx.android.parcel.Parcelize
@Parcelize
class User(var age: Int,var name: String): Parcelable

7. Simplify singleton object construction

Kotlin code (you can use object when defining the class name)

object User
{
    fun test()
    {
    }
}

java code

public final class User {
    public static final User instance = new User();

    public void test() {
    }

    public static User getInstance() {
        return instance;
    }

    private User() {
    }
}

8. Use string templates to simplify string concatenation

Kotlin code

val info = "name:$name,age:$age"

java code

String info = "name:" + name + ",age:" + age;

9. Use when for branch judgment (replacement of switch in Java)

Kotlin code

var id = 1
when (id) {
    1 -> print("x == 1")
    2 -> print("x == 2")
    else -> {
        print("id 不是 1 ，也不是 2")
    }
}

In addition, kotlin also supports writing conditions of the same class together, such as2,3 -> print("x == 2或者3")

java code

int x = 1;
switch (x) {
    case 1:
        print("x==1");
        break;
    case 2:
        print("x==2");
        break;
    default:
        print("id 不是 1 ，也不是 2");
        break;
}

10. Destructuring Objects ( Destructuring Declarations ) (Java does not have this advanced gameplay)

data class User(val username: String, val age: Int)
fun main() {
    val user = User("Jerry", 18)
    val (username, age) = user
    println("username:$username,age:$age")
}

11. Coroutines

The main advantage of the coroutine is not to reduce the code, but to simplify the calling logic, so that we don't have to use complex solutions such as AsyncTask or RxJava.

GlobalScope.launch {
    doSomething()
    withContext(Dispatchers.Main)
    {
        textView.text = "coroutines完成执行"
        Toast.makeText(this@MainActivity, "coroutines hooray", Toast.LENGTH_SHORT).show()
    }
}

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Advantages and disadvantages of Kotlin compared to Java