scala case 之类与对象

简介

本文主要介绍case class与普通class的一些区别。以及case class与case object的异同点。

case class与class的区别

Person.scala源码，运行后生成Person$.class和Person.class两个文件。

case class Person(age:Int, name:String)

object Person {
  def main(args: Array[String]): Unit = {
    val person = Person(25,"stm")
    println(person.toString)
  }
}

对Person.class反编译如下：

import scala.Function1;
import scala.Option;
import scala.Product;

package com.stm.datastructures.caseClass;

class;
import scala.Serializable;
import scala.Tuple2;
import scala.collection.Iterator;
import scala.reflect.ScalaSignature;
import scala.runtime.BoxesRunTime;
import scala.runtime.ScalaRunTime.;
import scala.runtime.Statics;

@ScalaSignature
public class Person
        implements Product, Serializable {
    private final int age;
    private final String name;

    public Person(int age, String name) {
        Product.class.$init$(this);
    }

    public boolean equals(Object x$1) {
        if (this != x$1) {
            Object localObject = x$1;
            int i;
            if ((localObject instanceof Person)) {
                i = 1;
            } else {
                i = 0;
            }
            if (i == 0) {
                break label96;
            }
            Person localPerson = (Person) x$1;
            if (age() == localPerson.age()) {
                str = localPerson.name();
                String tmp54_44 = name();
                if (tmp54_44 == null) {
                    tmp54_44;
                    if (str == null) {
                        break label75;
                    }
                    tmpTernaryOp = tmp54_44;
                    break label88;
                }
            }
        }
    }

    public String toString() {
        return ScalaRunTime..MODULE$._toString(this);
    }

    public int hashCode() {
        int i = -889275714;
        i = Statics.mix(i, age());
        i = Statics.mix(i, Statics.anyHash(name()));
        return Statics.finalizeHash(i, 2);
    }

    public boolean canEqual(Object x$1) {
        return x$1 instanceof Person;
    }

    public Iterator<Object> productIterator() {
        return ScalaRunTime..MODULE$.typedProductIterator(this);
    }

    public Object productElement(int x$1) {
        int i = x$1;
        switch (i) {
            default:
                throw new IndexOutOfBoundsException(BoxesRunTime.boxToInteger(x$1).toString());
            case 1:
                break;
        }
        return BoxesRunTime.boxToInteger(age());
    }

    public int productArity() {
        return 2;
    }

    public String productPrefix() {
        return "Person";
    }

    public String copy$default$2() {
        return name();
    }

    public int copy$default$1() {
        return age();
    }

    public Person copy(int age, String name) {
        return new Person(age, name);
    }

    public String name() {
        return this.name;
    }

    public int age() {
        return this.age;
    }

    public static Function1<Object, Function1<String, Person>> curried() {
        return Person..MODULE$.curried();
    }

    public static Function1<Tuple2<Object, String>, Person> tupled() {
        return Person..MODULE$.tupled();
    }

    public static Person apply(int paramInt, String paramString) {
        return Person..MODULE$.apply(paramInt, paramString);
    }

    public static Option<Tuple2<Object, String>> unapply(Person paramPerson) {
        return Person..MODULE$.unapply(paramPerson);
    }
}

对Person$.class编译如下：

import scala.Option;
import scala.Serializable;
import scala.Some;
import scala.Tuple2;
import scala.runtime.AbstractFunction2;
import scala.runtime.BoxesRunTime;

public final class Person$
        extends AbstractFunction2<Object, String, Person>
        implements Serializable {
    public static final MODULE$;

    private Person$() {
        MODULE$ = this;
    }

    private Object readResolve() {
        return MODULE$;
    }

    public Option<Tuple2<Object, String>> unapply(Person x$0) {
        return x$0 == null ? None..MODULE$:
        new Some(new Tuple2(BoxesRunTime.boxToInteger(x$0.age()), x$0.name()));
    }

    public Person apply(int age, String name) {
        return new Person(age, name);
    }

    public final String toString() {
        return "Person";
    }

    static {
        new ();
    }
}

Student.scala源码，运行后生成Student$.class和Student.class两个文件。

class Student(val age:Int, val name:String){}

object Student{
  def main(args: Array[String]): Unit = {
    val stu = new Student(25, "stm")
    println(stu)
  }
}

对Student.class反编译如下:

import scala.reflect.ScalaSignature;

@ScalaSignature
public class Student {
    private final int age;
    private final String name;

    public Student(int age, String name) {
    }

    public String name() {
        return this.name;
    }

    public int age() {
        return this.age;
    }

    public static void main(String[] paramArrayOfString) {
        Student..MODULE$.main(paramArrayOfString);
    }
}

对Student$.class反编译如下:

import scala.Predef.;

public final class Student$ {
    public static final MODULE$;

    static {
        new ();
    }

    public void main(String[] args) {
        Student stu = new Student(25, "stm");
        Predef..MODULE$.println(stu);
    }

    private Student$() {
        MODULE$ = this;
    }
}

从编译结果，可以看出一下几点：

1. 生成了apply方法，可以直接把对象当做方法使用。

   val person = Person(25,"stm")

2. 继承了Product和Serializable。

3. age和name是用final修饰的。
4. 默认实现了toString。

5. 实现了name()和age()方法。（参数列表中的参数都隐式获得一个val作为前缀）

   println(person1.age) //25
   println(person1.name) //stm

6. 重写了equals方法，比较structure而不是reference:

   val person1 = Person(25, "stm")
   val person2 = Person(25, "stm")
   println(person1 == person2) //true

case object与case class区别

1. case object反编译后没有apply和unapply方法，因为caes object没有参数。

总结

1. case class和case object本质没区别，有参使用case class，无参使用case object;
2. case class和case object增加了继承和方法。
3. case class和case object支持模式匹配。