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Using the Java API
Where’s the API?
General approach
• If you know the name of the package, click it in the
upper left panel; or click All Classes
• Click on the class in the lower left panel
• Scroll in the right pane to find the summary of the
field, method, or constructor you want
– Or just read the general description
• For more information, click the link in the
summary to go to the detailed information
The Packages panel
• Choose the package you are
interested in
• Or, choose All Classes
• Classes in java.lang are
automatically imported into
every program--you don’t
have to do it yourself
The Classes panel
• This panel shows both
classes and interfaces
• We haven’t yet talked about
• Note that some classes have
names similar to primitive
types (Boolean, Byte,
The links bar
Overview is where you start out
Index is handy for looking up methods
Help is the obvious
If you don’t like frames, you can choose
• Deprecated methods are those that have been
replaced by better methods and should not be used
The main information area
General description of the class
Field summary
• In each case, the
Constructor summary
“summary” is the first
Method summary
sentence of the “detail”
Field detail
Constructor detail
Method detail
Reading the method descriptions I
• An example from the String class:
– public char charAt(int index)
• Returns the character at the specified index
public means accessible from anywhere
char is the return type
charAt is the name of the method
int is the type of parameter expected
index is just a suggestive name
Example use: char firstChar = myStr.charAt(0);
Reading the method descriptions II
• Another example from the String class:
– public static String valueOf(int i)
• Returns the string representation of the int argument.
public means accessible from anywhere
static means this is a class method (see use below)
String is the return type, and is a hyperlink
valueOf is the name of the method
int is the type of parameter expected
i is just a suggestive name
– Example use: String numeral = String.valueOf(m / n);
How was this documentation
• All Java documentation was produced by the
javadoc program from javadoc (or just doc)
comments in the source code
• Your doc comments can be used in the same way
to produce professional-looking documentation
• The Interface menu item in BlueJ does the same
basic thing as javadoc
– Like most things in BlueJ, fancy features have
been omitted in the interests of simplicity
Value of the API
• Version
Java 1.0
Java 1.1
Java 1.2
Java 1.3
Java .14
• You can only learn a small fraction of these
• When you learn the kinds of things that are in the API, and
learn to find your way around in it, you become a far more
effective and efficient programmer
• A good craftsman knows his/her tools
The End