Java Coding Practices

R.SANTHANA GOPALAN

Java Coding Practices

Avoid call method inside the “for” loop Wrong

for( int i =0; i < vec.size(); i++){

...}

Unnecessary vec.size() will be called every time the loop continues. We can store the vec.size() in a “int” datatype and we can use in a “for” loop.

Correctint vec_size=vec.size();for(int i =0; i < vec_size; i++){

...}

Wrong Example:boolean b = threadObj.isAlive();

for( ; b; )

{

….

}

Java Coding Practices

Avoid Recursive Method If possible try to avoid Recursive method

calling. If you don’t know the limit then the

StackOverFlow error will happen.

Java Coding Practices

isVisible() -or- getVisible() If the method returns the boolean value then

the method name should be starts with “is”. If the method returns non-boolean value

then the method name should be starts with “get”. Eg. getBackground().

Java Coding Practices

Converter Method Initial lowercase word is "to", remaining

subwords are capitalized.Example:

toGenie(), toTiger(),

Java Coding Practices

Getters Methodmethods that query state. Initial lowercase word is "get", remaining

sub words are capitalized and, if possible, are exactly the same as the name of the instance field to which they relate.

Example:getDjinnName(), getCatColor()

Java Coding Practices

Setters Methodmethods that set state Initial lowercase word is "set", remaining

sub-words are capitalized and, if possible, are exactly the same as the name of the instance field to which they relate.

Example: setDjinnLocation()

Java Coding Practices

Method – pass by reference (or) value?Be very careful by passing the Objects to

the another method. If the method changes the value in the

method then make sure that is documented.

Java Coding Practices

Do you know the answer?public void tricky(Point arg1, Point arg2){

arg1.x = 100;arg1.y = 100;

Point temp = arg1; arg1 = arg2; arg2 = temp;

}

public static void main(String [] args) {

Point pnt1 = new Point(0,0); Point pnt2 = new Point(0,0); System.out.println("X: " + pnt1.x + " Y: " +pnt1.y); System.out.println("X: " + pnt2.x + " Y: " +pnt2.y); System.out.println(" "); tricky(pnt1,pnt2); System.out.println("X: " + pnt1.x + " Y:" + pnt1.y); System.out.println("X: " + pnt2.x + " Y: " +pnt2.y);

}

Java Coding Practices

Answer:X: 0 Y: 0

X: 0 Y: 0

X: 100 Y: 100

X: 0 Y: 0

Avoid this kind of programming.

Java Coding Practices

If you override Object.equals(), also override Object.hashCode(), and vice-versa.

Reason:Essentially all containers and other utilities

that group or compare objects in ways depending on equality rely on hashcodes to indicate possible equality.

Java Coding Practices

Import classes one by one instead of importing a whole package, thus it becomes clearer.

Example: import com.adventnet.beans.graph.LineGraph; import com.adventnet.beans.graph.BarGraph;

Java Coding Practices

Don’t declare variables as package level access. The default access level is package.Wrong

int status;Correct

private int status;

Java Coding Practices

if” (or) “else if” - Document it perfect.Example:

if(prop.containsKey("caseid")){ //Do some action}if(prop.containsKey("casemessage")){ //Do some action}

Java Coding Practices

Keep the block level less than 4.Wrong Example:

if (condition1){ if(condition2) { if(condition3) { if(condition 4) { if (condition5) {

Java Coding Practices

Don’t call the method unnecessarilyWrong Example:

if(ae.getA().equals("Default"))

{

}

else if(ae.getA().equals(“One”))

{

}

Java Coding Practices

CorrectString aVal=ae.getA();

if(aVal.equals("Default"))

{

}

else if(aVal.equals(“One”))

{

}

Java Coding Practices

Don’t use “\n” for the new line characterWrong Example:

textarea.append(message + “\n”);Correct Example:

Declare private static String lineseparator = System.getProperty(“lineseparator”);

textarea.append(message + lineseparator);

Java Coding Practices

Use File.separator for the file separator. If it is really required then use “/”.Wrong

fname=“help/index.html”Correct

fname=“help” +File.separator + “index.html”

Java Coding Practices

Be careful while add the debug statements in StringTokenizer.nextToken()Wrong Example

StringTokenizer st = new StringTokenizer(strValue)while(st.hasMoreElements()){ String s = st.nextToken(); System.out.println(st.nextToken()); -----}

Java Coding Practices

StringBuffer - Performance If you know the size then instantiate

StringBuffer(int n). This will give high performance.

Java Coding Practices

FileOutput Stream is costly. Wrong

fos = new FileOutputStream(f);

fos.write(htmltagstart.getBytes());

fos.write(headtagstart.getBytes());

fos.write(metatag.getBytes());

Java Coding Practices

Correct

StringBuffer sb = new StringBuffer(1000);sb.append(htmltagstart);sb.append(headtagstart);sb.append(metatag);

fos = new FileOutputStream(f);fos.write(sb.toString().getBytes());

Java Coding Practices

Do proper close operation. Otherwise it will create lot of problem in the runtime.Example:

FileOutStream.close()ResultSet.close()

Java Coding Practices - Question

FileInputStream: read() Vs. read(byte[]) . Which will give more performance?

FileOutputSteam: write() Vs. write(byte[]). Which will give more performance?

Java Coding Practices

SerializableSerialization can be very costly.Using the transient keyword reduces the

amount of data serialized.

Wrong Example:private JFrame;

Correct Example:private transient JFrame;

Java Coding Practices

Explicitly set the layout of the panel/Frame/Dialog. Don’t leave it to default.Panel.setLayout(new BorderLayout());

Java Coding Practices

Use the Constant to add the component in BorderLayout.Wrong Example:

panel.add(“Center”,textarea);Correct Example:

panel.add(textarea,BorderLayout.CENTER);

Java Coding Practices

Don’t call UIManager.setLookAndFeel() in your program. Only the main class can call this method.UIManager.getCrossPlatformLookAndFeelC

lassName());

Java Coding Practices - Question

What is wrong?

private int sum;

public CalculateSum(int sum)

{

sum=sum;

}

Java Coding Practices

JOptionPane(Object,…) - What is the difference between passing “null” value and passing the exact JFrame object?

Java Coding Practices

Don’t write anonymous classesWrong:

textarea.addActionListener(new ActionListener(){

…….

…….

};

Java Coding Practices

Don’t use “goto” command and “labelled” statements.

Java Coding Practices

Use Bean Builder to develop UI.….features

Java Coding Practices

Common MistakeComparing String using “==“ operator.