Commons Collection 3 - Buffer

Queue, Stack, Binary Heap

Bufferはスタック，キュー及びバイナリヒープの機能を提供する．
標準ライブラリにもスタック，キューはあるのでわざわざこちらを使う必要があるかどうか．．の判断は私たち次第である．

コード

この例ではキューとしてUnboundedFifoBuffer, スタックとしてArrayStack, バイナリヒープとしてPriorityOrderを使っている．

import java.util.Comparator;

import org.apache.commons.collections.ArrayStack;
import org.apache.commons.collections.Buffer;
import org.apache.commons.collections.buffer.PriorityBuffer;
import org.apache.commons.collections.buffer.UnboundedFifoBuffer;
import org.junit.Test;
import static org.junit.Assert.*;
import static org.hamcrest.CoreMatchers.*;

public class CollectionsTest {

 @Test
 public void testBuffer() {
  // Queue - FIFO
  Buffer buffer = new UnboundedFifoBuffer();
  injectTestValue( buffer );
  assertThat( (String)buffer.get(), is( "1st" ) );
  assertThat( (String)buffer.remove(), is( "1st" ) );
  assertThat( (String)buffer.remove(), is( "2nd" ) );
  assertThat( (String)buffer.remove(), is( "3rd" ) );
  // Stack - LIFO
  buffer = new ArrayStack();
  injectTestValue( buffer );
  assertThat( (String)buffer.get(), is( "3rd" ) );
  assertThat( (String)buffer.remove(), is( "3rd" ) );
  assertThat( (String)buffer.remove(), is( "2nd" ) );
  assertThat( (String)buffer.remove(), is( "1st" ) );
  // BinaryHeap
  // ascending
  buffer = new PriorityBuffer( true, new StringLengthComparator<String>() );
  injectTestValueForPriorityBuffer( buffer );
  assertThat( (String)buffer.remove(), is( "/usr" ) );
  assertThat( (String)buffer.remove(), is( "/usr/local" ) );
  assertThat( (String)buffer.remove(), is( "/usr/local/bin" ) );
  // descending
  buffer = new PriorityBuffer( false, new StringLengthComparator<String>() );
  injectTestValueForPriorityBuffer( buffer );
  assertThat( (String)buffer.remove(), is( "/usr/local/bin" ) );
  assertThat( (String)buffer.remove(), is( "/usr/local" ) );
  assertThat( (String)buffer.remove(), is( "/usr" ) );
 }
 
 private void injectTestValue( Buffer buffer ) {
  buffer.add( "1st" );
  buffer.add( "2nd" );
  buffer.add( "3rd" );
 }
 
 private void injectTestValueForPriorityBuffer( Buffer buffer ) {
  buffer.add( "/usr" );
  buffer.add( "/usr/local" );
  buffer.add( "/usr/local/bin" );
 }

}

class StringLengthComparator<String> implements Comparator<String> {


 public int compare( String arg0, String arg1 ) {
  
  if( ((java.lang.String) arg0).length() > ((java.lang.String) arg1).length() )
   return 1;
  else if( ((java.lang.String) arg0).length() == ((java.lang.String) arg1).length() )
   return 0;
  else
   return -1;
  
 }
 
}