JavaBeans ​

In Java, there are many class definitions that conform to this specification:

• Several private instance fields;
• Read and write instance fields through public methods.

For example:

public class Person {
    private String name;
    private int age;

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

    public int getAge() { return this.age; }
    public void setAge(int age) { this.age = age; }
}

If the read and write methods conform to the following naming convention:

// Reading method:
public Type getXyz()
// write method:
public void setXyz(Type value)

Then this class is called JavaBean :

The above field is xyz , then the read and write method names start with get and set respectively, and are followed by the field name Xyz starting with an uppercase letter, so the two read and write method names are getXyz() and setXyz() respectively.

The boolean field is special, and its reading method is generally named isXyz() :

// Reading method:
public boolean isChild()
// write method:
public void setChild(boolean value)

We usually refer to a set of corresponding read methods ( getter ) and write methods ( setter ) as properties ( property ). For example, the name attribute:

• The corresponding reading method is String getName()
• The corresponding writing method is setName(String)

Properties with only getter are called read-only properties. For example, define an age read-only property:

• The corresponding reading method is int getAge()
• There is no corresponding writing method setAge(int)

Similarly, properties with only setter are called write-only properties.

Obviously, read-only properties are common and write-only properties are uncommon.

Properties only need to define getter and setter methods, and do not necessarily need corresponding fields. For example, child read-only property is defined as follows:

public class Person {
    private String name;
    private int age;

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

    public int getAge() { return this.age; }
    public void setAge(int age) { this.age = age; }

    public boolean isChild() {
        return age <= 6;
    }
}

It can be seen that getter and setter are also a method of data encapsulation.

The role of JavaBeans ​

JavaBean is mainly used to transfer data, that is, to combine a set of data into a JavaBean for easy transmission. In addition, JavaBean can be easily analyzed by IDE tools to generate code for reading and writing properties, which is mainly used in the visual design of graphical interfaces.

Through the IDE, getter and setter can be quickly generated. For example, in Eclipse, first enter the following code:

public class Person {
    private String name;
    private int age;
}

Then, right-click, select "Source", "Generate Getters and Setters" in the pop-up menu, select the fields that need to generate getter and setter methods in the pop-up dialog box, click OK, and the IDE will automatically complete all method codes.

Enumeration JavaBean properties ​

To enumerate all properties of a JavaBean, you can directly use Introspector provided by the Java core library:

import java.beans.*;

public class Main {
    public static void main(String[] args) throws Exception {
        BeanInfo info = Introspector.getBeanInfo(Person.class);
        for (PropertyDescriptor pd : info.getPropertyDescriptors()) {
            System.out.println(pd.getName());
            System.out.println("  " + pd.getReadMethod());
            System.out.println("  " + pd.getWriteMethod());
        }
    }
}

class Person {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

Running the above code will list all attributes and corresponding read and write methods. Note that the class attribute is brought by the getClass() method inherited from Object .

Summary ​

JavaBean is a class that conforms to naming conventions and defines properties through getter and setter ;

Attribute is a common name and is not specified by Java grammar;

You can use IDE to quickly generate getter and setter ;

Use Introspector.getBeanInfo() to get the property list.