Tag Archives for " Core Java "

Comparable vs Comparator Comparison

java.lang.Comparable

[sourcecode language=”java”]

Comparable.compareTo(Object toCompare)

[/sourcecode]

• Natural ordering – eg List of Users ordered by Id
• Implemented against class
• Sorting Method – int compareTo(Object o1)
• CurrentObject vs compareToObject
• compareTo return –

          1. positive – if ( currentObject > compareToObject)

         2. zero – if ( currentObject == compareToObject)

         3. negative – if ( currentObject < compareToObject)

[sourcecode language=”java”] public class Bicycle implements Comparable {

private int size;

public void setSize(int size) {

this.size = size;

}

public int getSize() {

return size;

}

@Override
public int compareTo(Object arg0) {

Bicycle bicycleCompareTo =(Bicycle) arg0;

if ( this.bicycleId > bicycleCompareTo.bicycleId ) {

return 1;

} else if ( this.bicycleId < bicycleCompareTo.bicycleId ) {

return -1;

} else {

return 0;

}

}

}
[/sourcecode]

• Calling method –

[sourcecode language=”java”]

Collections.sort(List)

[/sourcecode]

　

　

java.util.Comparator

• Alternative ordering – eg List of Bicycles ordered by BikeSize
• Multiple Comparators

[sourcecode language=”java”]

Comparator.compare(Object obj1, Object obj2)

[/sourcecode]

• Nested static classes
• Sorting Method – int compare(Object o1, Object o2)

          1. positive – if ( o1 > o2 )

          2. zero – if ( o1 == o2 )

          3. negative – if ( o1 < o2 )

• Calling –

[sourcecode language=”java”]

Collections.sort(List, Comparator)

[/sourcecode]

• Example –

[sourcecode language=”java”] public class BicycleSizeComparator implements Comparator<Bicycle>{

@Override
public int compare(Bicycle bicycle1, Bicycle bicycle2) {

if ( bicycle1.getSize() > bicycle2.getSize() ) {

return 1;

} else if ( bicycle1.getSize() < bicycle2.getSize() ) {

return -1;

} else {

return 0;

}

}

}
[/sourcecode]