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Data Fields of Java Objects

Access Public and Private Data

Java® classes can contain member variables called fields which might have public or private access.

To access public data fields, which your code can read or modify directly, use the syntax:

object.field

To read from and, where allowed, to modify private data fields, use the accessor methods defined by the Java class. These methods are sometimes referred to as get and set methods.

For example, the java.awt.Frame class has both private and public data fields. The read accessor method getSize returns a java.awt.Dimension object.

frame = java.awt.Frame;
frameDim = getSize(frame)

frameDim =

java.awt.Dimension[width=0,height=0]

The Dimension class has public data fields height and width. Display the value of height.

height = frameDim.height

height = 0

Set the value of width.

frameDim.width = 42
frameDim =

java.awt.Dimension[width=42,height=0]

Display Public Data Fields of Java Object

To list the public fields of a Java object, call the fieldnames function. For example, create an Integer object and display the field names.

value = java.lang.Integer(0);
fieldnames(value)
ans = 
    'MIN_VALUE'
    'MAX_VALUE'
    'TYPE'
    'SIZE'

To display more information about the data fields, type:

fieldnames(value,'-full')
ans = 
    'static final int MIN_VALUE'
    'static final int MAX_VALUE'
    'static final java.lang.Class TYPE'
    'static final int SIZE'

Access Static Field Data

A static data field is a field that applies to an entire class of objects. To access static fields, use the class name. For example, display the TYPE field of the Integer class.

thisType = java.lang.Integer.TYPE
thisType =

int

Alternatively, create an instance of the class.

value = java.lang.Integer(0);
thatType = value.TYPE
thatType =

int

MATLAB® does not allow assignment to static fields using the class name. To assign a value, use the static set method of the class or create an instance of the class. For example, assign value to the following staticFieldName field by creating an instance of java.className.

objectName = java.className;
objectName.staticFieldName = value;

See Also