Java memo

For memorandum.


DeepCopy DeepCopy by java.util.Arrays

int[] copySrc = new int[5];
Arrays.fill(copySrc, 0);
int[] copyDst = Arrays.copyOf(copySrc, copySrc.length);

DeepCopy of object

DeepCopy by org.apache.commons.lang3.SerializationUtils # clone

public Object deepCopy(Serializable state) {
  return SerializationUtils.clone(state);

Priority Queue --PriorityQueue

I don't know how to use it effectively. It seems to be useful for solving AtCoder Regular Contest 028 --B --Special Award.

PriorityQueue<Integer> pQueue = new PriorityQueue<Integer>();
pQueue.offer(i);    //add to
pQueue.peek(i);     //Get (do not remove from queue)
pQueue.poll(i);     //Get (remove from queue)

Show the contents of the object

// commons-lang
System.out.println(ToStringBuilder.reflectionToString(new Hoge()));
// [email protected][id=1,value=hoge,strValues={aaa,bbb,ccc},items=[ddd, eee, fff]]

Give the object a hash code

public class Clazz implements Serializable {
  private static final long serialVersionUID = 1L;
  public int hashCode() {
    return HashCodeBuilder.reflectionHashCode(this);

You can easily write an object match judgment

public class Hoge implements Serializable {
    private static final long serialVersionUID = 1L;
    public int getId() {
        return id;
    public void setId(int id) { = id;
    public boolean equals(Object obj) {
        return EqualsBuilder.reflectionEquals(this, obj);

Category value judgment

Use Enum. That's right ~

if ( Arrays.asList("Cat", "Dog", "Pig").contains(hoge) ) {
  // Do somthings.

List initialization

List<String> list = new ArrayList<>(Arrays.asList("Cat", "Dog", "Pig"));

Ascending sort of file name

//File name sort in ascending order
List<File> csvFileList = new ArrayList<File>();
csvFileList.add( new File("###") );
csvFileList.add( new File("BBB") );
csvFileList.add( new File("111") );
csvFileList.add( new File("AAA") );

Collections.sort( csvFileList, new Comparator<File>(){
   public int compare( File o1, File o2 ) {
       return o1.getName(), o2.getName() );

IterableUtils.forEach( csvFileList, new Closure<File>(){
   public void execute( File file ) {
       System.out.println( ReflectionToStringBuilder.toString( file ) );


Get resource file

ResourceLoader resourceLoader;

final Resource resource = resourceLoader.getResource("classpath:path/to/file");

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