Six Ways to Create Objects in Java

Background: The author wishes programmers a happy Valentine’s Day and introduces six ways to create objects in Java, ranging from the simplest to more advanced techniques.

Method 1: Create an object with new

Using the new keyword is the most straightforward way to instantiate a class.

@Data
@NoArgsConstructor
@AllArgsConstructor
class GirlFriend {

  private String name;

}

/**
 * new an object
 */
@Test
public void girlFriend1() {
    GirlFriend girlFriend = new GirlFriend("new一个对象");
    System.out.println(girlFriend);
}

GirlFriend(name=new一个对象)

Method 2: Clone an object

Implement Cloneable and override clone() to produce a shallow copy.

@Data
@NoArgsConstructor
@AllArgsConstructor
class GirlFriend implements Cloneable {

  private String name;

  @Override
  protected Object clone() throws CloneNotSupportedException {
      return super.clone();
  }
}

@Test
public void girlFriend2() throws CloneNotSupportedException {
    GirlFriend girlFriend1 = new GirlFriend("克隆一个对象");
    GirlFriend girlFriend2 = (GirlFriend) girlFriend1.clone();
    System.out.println(girlFriend2);
}

GirlFriend(name=克隆一个对象)

Method 3: Allocate an object via reflection (Class.newInstance())

@Test
public void girlFriend3() throws InstantiationException, IllegalAccessException {
    GirlFriend girlFriend = GirlFriend.class.newInstance();
    girlFriend.setName("类派发一个对象");
    System.out.println(girlFriend);
}

GirlFriend(name=类派发一个对象)

Method 4: Load and instantiate an object dynamically (Class.forName())

@Test
public void girlFriend4() throws InstantiationException, IllegalAccessException, ClassNotFoundException {
    GirlFriend girlFriend = (GirlFriend) Class.forName("cn.javastack.test.jdk.core.GirlFriend").newInstance();
    girlFriend.setName("反射一个对象");
    System.out.println(girlFriend);
}

GirlFriend(name=反射一个对象)

Method 5: Construct an object via reflection (Constructor.newInstance())

@Test
public void girlFriend5() throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
    GirlFriend girlFriend = GirlFriend.class.getConstructor().newInstance();
    girlFriend.setName("构造一个对象");
    System.out.println(girlFriend);
}

GirlFriend(name=构造一个对象)

Method 6: Deserialize an object

Make the class implement Serializable and use standard Java serialization APIs.

@Data
@NoArgsConstructor
@AllArgsConstructor
class GirlFriend implements Cloneable, Serializable {
    private static final long serialVersionUID = 1L;
    private String name;
    @Override
    protected Object clone() throws CloneNotSupportedException { return super.clone(); }
}

@Test
public void girlFriend6() throws IOException, ClassNotFoundException {
    GirlFriend girlFriend1 = new GirlFriend("反序列化一个对象");
    // Serialize
    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("gf.obj"));
    oos.writeObject(girlFriend1);
    oos.close();
    // Deserialize
    ObjectInputStream ois = new ObjectInputStream(new FileInputStream("gf.obj"));
    GirlFriend girlFriend2 = (GirlFriend) ois.readObject();
    ois.close();
    System.out.println(girlFriend2);
}

GirlFriend(name=反序列化一个对象)

All example code is available on the author’s GitHub repository, and readers are encouraged to try these techniques or share other object‑creation methods.