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Arrays.equals without length of arrays

I have two arrays with different length, but same elements. For example
A1 = {1,2,3,null,null}
A2 = {1,2,3}
Arrays.equals gives me false, because arrays have different length. Are there any method in java that will compare only elements in method?
I don't want to use .toString
I'm trying to make compare method in my own generic stack realization.

No, because its a weird request. null does not mean 'not here', null means 'unknown / unset', that's why it throws exceptions when you interact with it: You're asking "hey, thing that has not been set yet, are you X", and there is no way to answer such a question.
That doesn't mean your code is wrong, just, you can stop looking for existing implementations. Weird requests generally aren't catered to by the core libraries (or any other). You also may want to change your mindset on null. Programming in java is a lot less aggravating if at all times a NullPointerException is a good thing. In other words, avoid using null as having any semantic meaning. If you ever write if (x == null || x.isEmpty()) you are doing it wrong. Instead, where-ever 'x' is coming from, it should hold, or be updated to ASAP, the empty string instead. So, if reading in external data (e.g. you marshalled some JSON into an object), do a 'clean' step that replaces all null values that have semantic meaning with an object that actually represents it, and for methods that return stuff, always return an object that represents what you are returning - only return null if you WANT to convey the notion that there is no result (i.e. that's not the same as 'an empty result', i.e. if any code acts like there was a result, you want it to crash).
In other words, I doubt you are asking the right question. But in case you are, you have two broad options.
First make null-less arrays then compare those as normal
One option is to make new arrays that have nulls stripped. Something like:
#SuppressWarnings("unchecked")
<T> T[] stripNulls(T[] in) {
Class<?> componentType = in.getClass().getComponentType();
return (T[]) Arrays.stream(in)
.filter(x -> x != null)
.toArray(len -> java.lang.reflect.Array.newInstance(componentType, len));
}
// which you can then use; you don't need generics for a compare,
// it wouldn't add anything at all.
boolean compare(Object[] a, Object[] b) {
return Arrays.equals(stripNulls(a), stripNulls(b));
}
Just compare in place
If it's performance sensitive that's suboptimal. A better approach would involve a little more coding:
boolean compare(Object[] a, Object[] b) {
Object ae = null, be = null;
int ai = 0, bi = 0, al = a.length, bl = b.length;
while (true) {
/* set `ae` and `be` to the next non-null element */
while (ae == null && ai < al) ae = a[ai++];
while (be == null && bi < bl) be = b[bi++];
/* Have we hit the end? */
if (ai == al && bi == bl) return true;
/* If one is at the end, but the other isn't... */
if (ai == al || bi == bl) return false;
/* check if the 2 current elements are equal */
if (!ae.equals(be)) return false;
}
}

Not a native Java Developer, but maybe this helps you?
boolean arraysEqual = Arrays.equals(Arrays.stream(a1).filter(n => n != null).toArray(), Arrays.stream(a2).filter(n => n != null).toArray())

Custom Java Comparator With Pre Defined Top Result

I want to sort a list of field names alphabetically however I need to include a condition in the doCompare method of the comparator so that if the field name is "pk" that will always be sorted to the top of the list. What I have is below but I'm not sure if I'm taking the right approach, particualrly with the reurn value of -1000. Any advice on this would be much appreciated.
#Override
public int doCompare(Object firstRec, Object secondRec)
{
MyField firstField = (MyField) firstRec;
MyField secondField = (MyField ) secondRec;
if(firstField.name() == "pk")
{
return -1000;
}
return StringUtils.compareStrings(firstField.name().toLowerCase(), secondField.name().toLowerCase());
}

The requirements of a Comparator (and, by extension, methods which are supposed to act like Comparator.compare) are described in the Javadoc:
The implementor must ensure that sgn(compare(x, y)) == -sgn(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.)
The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0.
Finally, the implementor must ensure that compare(x, y)==0 implies that sgn(compare(x, z))==sgn(compare(y, z)) for all z.
Assuming StringUtils.compareStrings correctly implements these requirements, the thing you've got wrong is the first requirement: you also need to consider the cases when secondField is also pk:
The general pattern for writing correct Comparators is:
int firstComparison = /* compare something about firstField and secondField */;
if (firstComparison != 0) {
return firstComparison;
}
int secondComparison = /* compare something else about firstField and secondField */;
if (secondComparison != 0) {
return secondComparison;
}
// ...
return 0;
Applying that here:
int pkComparison = Boolean.compare(secondField.name().equals("pk"), firstField.name().equals("pk"));
if (pkComparison != 0) {
return pkComparison;
}
int compareStringsComparison = StringUtils.compareStrings(firstField.name().toLowerCase(), secondField.name().toLowerCase());
if (compareStringsComparison != 0) {
return compareStringsComparison;
}
return 0;
Obviously, the last if statement is redundant, because you always return compareStringsComparison whether or not it is zero; so you could write simply:
return StringUtils.compareStrings(firstField.name().toLowerCase(), secondField.name().toLowerCase());
I would recommend sticking to the compare/check and return/finally return 0 pattern, because it's easier to slot in additional conditions later. But it's not terrible either way.

The new static methods of class Comparator available since Java 8 are very handy to create a multi-criteria Comparator like in your case.
You could try something like this:
List<String> list = ... ;
list.sort(
Comparator.comparingBoolean("PK"::equals)
.thenComparing(StringUtils::compare)
);
You may need to use .reversed() in case the order is the opposite of what you want.
The great advantage of Comparator.comparing / Comparator.comparingXXX is that you don't need to twist your mind to get the correct behavior when to return a positive, negative or 0 value.
The Comparator.thenComparing dos proper chaining, i.e. it checks further criterias only when needed, only when previous comparisons returned 0.
If your list may contain null values, there are also methods to handle them properly. This isn't the case in this short example.

Determine IF statement condition at runtime

I have a function which accepts two parameters, foo(A a, String type) depending on type I have to change the if statement condition.
foo(A a, String type){
//if type equals 'bar'
if(!a.isEmpty() && a.hasMember()){...}
//but if type is something else
if(!a.isEmpty() || a.hasMember()){...}
}
the logic in the if body is the same pretty much everything else is the same except the condition is there any efficient way to implement the difference or I have to write everything twice?

I suppose you can use the following:
foo(A a, String type){
//if type equals 'bar'
if("bar".equals(type)) {
if(!a.isEmpty() && a.hasMember()){...}
}
else {
//but if type is something else
if(!a.isEmpty() || a.hasMember()){...}
}
}
Explanation: If type has value "bar" then if condition becomes true and then whatever code you want for that condition will be executed.
You can also use concise form:
if( ("bar".equals(type) && (!a.isEmpty() && a.hasMember())) || (!"bar".equals(type) && (!a.isEmpty() || a.hasMember()))) {
// Do your stuff
}
The point to note is "bar".equals(type) is better than type.equals("bar") as it also saves you from hassle of the case when type is null.

Combine the predicates with an || and make the check of type in each condition part.
if (type.equals("bar") && !a.isEmpty() && a.hasMember()) || (!type.equals("bar") && (!a.isEmpty() || a.hasMember())) {
//do your thing
}
If null is a possible value of type, then it is possible to change the check to "bar".equals(type) to avoid a NullPointerException.

You could use a map with key type, and value should be object that have you type related logic.
foo(A a, String type) {
typesMap.get(type).execute(a);
}
class TaskImpl implements Task { // each task should behave as it should be
#override
public void execute(A a) {
if(!a.isEmpty() && a.hasMember()) {...}
}
}

Best practice : get deep value of an object

Often in java I have to get a value of a property of an object which is deep in this object. For example, if I'm sure that all my sub-objects are not null, I can do that :
public function getDeepValue(A a) {
String value = a.getB().getC().getListeD().get(0).getE().getValue();
return value;
}
But in case of sub objects of the parent can be null, I have to test every object.
To do that, I see 2/3 solutions :
First, step by step :
public function getDeepValue(A a) {
if(a == null){
return null;
}
B b = a.getB();
if(b == null) {
return null;
}
C c = b.getC();
if(c == null){
return null;
}
List<D> ds = c.getListeD();
if(ds == null || ds.size() == 0){
return null;
}
D d = ds.get(0);
if(d == null) {
return null;
}
E e = d.getE()
if(e == null){
return null;
}
return e.getValue();
}
Second, test all in one if block, soooo dirty :
public function getDeepValue(A a) {
if(a != null && a.getB() != null && a.getB().getC() != null && a.getB().getC().getListeD() != null && a.getB().getC().getListeD().size() > 0 && a.getB().getC().getListeD().get(0) != null && a.getB().getC().getListeD().get(0).getE() != null){
return a.getB().getC().getListeD().get(0).getE().getValue();
}
return null;
}
Third solution, using a try catch block :
public function getDeepValue(A a) {
try {
return a.getB().getC().getListeD().get(0).getE().getValue();
} catch(NullPointerException e) {
return null;
} catch(IndexOutOfBoundsException e) {
return null;
}
}
Solution 1 seems not too bad but needs a lot of code. It is generally the solution I use.
Solution 2 is for me really dirty...
In paper, I realy like solution 3, but is it a good solution in term of performances ?
Is there any others acceptables solutions ?
Thanks for help, I hope my english is not too bad..
Regards

Solution #3 looks simple, but it can potentially hide a whole host of problems. It might be an adequate solution if you have full access to all of the classes in the chain and you know what's going on in each method and you can guarantee those methods won't cause problems with your try/catch and you're never going to change them... that's a lot of conditions to make it a worthwhile solution, but I can conceive that it's possibly a useful sufficient one.
Solution #2 looks horrid to me, especially if one or more of the get methods is a bottleneck (such as a slow database query or using a blocking network connection). The earlier in the chain such a potential bottleneck, the worse it would potentially be, as you're calling it over and over again. This of course depends on the implementation of the methods in question (even if one of them is slow, the result could be cached, for example), but you shouldn't need to know that in your client code. Even with efficient or trivial implementations, you've still got the overhead of repeated method calls you oughtn't need.
Solution #1 is the best of the three, but it's likely not the best possible. This solution takes more lines of code than the other two, but it doesn't repeat itself and it isn't going to be tripped up by the implementations of the other methods. (Note: If you do not have access to the classes in the chain for refactoring, I would use this solution.)
A better solution than #1 would be to refactor the classes so that the client code doesn't need to know about this chain at all. Something along these lines:
class Client {
public Mumble getDeepValue(A a) { return a == null ? null : a.getDeepValue(); }
}
class A {
private B b;
public Mumble getDeepValue() { return b == null ? null : b.getDeepValue(); }
}
class B {
private C c;
public Mumble getDeepValue() { return c == null ? null : c.getDeepValue(); }
}
class C {
private List<D> ds;
public Mumble getDeepValue() {
D d = ds == null || ds.size() == 0 ? null : ds.get(0);
return d == null ? null : d.getDeepValue();
}
}
class D {
private E e;
public Mumble getDeepValue() { return e == null ? null : e.getMumble(); }
}
class E {
private Mumble m;
public Mumble getMumble() { return m; }
}
As you can see, the longest chain any of these classes has is to access the public members of an element of a collection that is a private member of the class. (Essentially ds.get(0).getDeepValue()) The client code doesn't know how deep the rabbit hole goes, only that A exposes a method which returns a Mumble. Client doesn't even need to know that the classes B, C, D, E, or List exist anywhere!
Additionally, if I were designing this system from the ground up, I would take a good long look at whether it could be restructured such that the actual Mumble object wasn't so deep. If I could reasonably get away with storing the Mumble within A or B, I'd recommend doing it. Depending on the application, that may not be possible however.

in terms of performance solution 3 is the best one. In addition It is neat and easy to understand , For example looking at a loop example:
int[] b = somevalue;
for(int i=0;i<b.length;i++){
//do something
}
in this case for every iteration we execute the condition. However, there is another approach for it which uses try and catch
int[] b = somevalue;
try{
for(int i=0;;i++){
//do something
}
}catch(IndexOutOfBoundException e){
// do something
}
on the second solution,the loop keeps going until we reach the end of the loop which then it throws IndexOutOfBoundException as soon as we reach the end of the array. meaning we don't check for the condition no more. thus faster.

A cleaner if statement with multiple comparisons [closed]

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The following statement just looks very messy when you have a lot of terms:
if(a.equals("x") || a.equals("y") || a.equals("z") || Any number of terms...... )
//Do something
Is there a cleaner way of performing the same action, I would like my code to be as readable as possible.
NOTE: x, y and z are just placeholders for any string of any length. There could be 20 string terms here of variable length in if condition each being OR'd together

What do you think looks "unclean" about it?
If you have a bunch of complicated boolean logic, you might separate the different parts of it into individual boolean variables and refer to them in the if statement.
Or you could create a function that takes your 'a' variable and returns a boolean. You'd just be hiding your logic in the method, but it would clean up your if statement.

Set<String> stuff = new HashSet<String>();
stuff.add("x");
stuff.add("y");
stuff.add("z");
if(stuff.contains(a)) {
//stuff
}
If this is a tight loop you can use a static Set.
static Set<String> stuff;
static {
stuff = new HashSet<String>();
stuff.add("x");
stuff.add("y");
stuff.add("z");
}
//Somewhere else in the cosmos
if(stuff.contains(a)) {
//stuff
}
And if you want to be extra sure nothing is getting modified while you're not looking.
Set<String> test = Collections.unmodifiableSet(new HashSet<String>() {
{
add("x");
add("y");
add("z");
}
});
If you just want to get some logic in there for a handful of hard coded conditions then one of the switch or if statement with newlines solutions might be better. But if you have a lot of conditions then it might be good to separate your configuration from logic.

Alternatively, if you are using Java 7+ you can use strings in switch/case. For example (I extracted this from an Oracle doc and modified)
switch (str) {
case "x":
case "y":
case "z":
//do action
break;
default:
throw new IllegalArgumentException("argument not matched "+str);
}
Here is the link

Use a regular expression
If (a.matches("[xyz]")){
// matches either "x", "y", or "z"
or, for longer strings,
If (a.matches("one|two|three")){
// matches either "one", "two" or "three"
But this is computationally expensive, but probably not much worse than instantiating a set etc. But it's the clearest way I can think of.
But in the end, the nicest way is probably to leave things as they are, with an adjustment to the formatting:
if (a.equals("x") ||
a.equals("y") ||
a.equals("z")
){
There is then absolutely no ambiguity in what the code is doing and so your code will be easier to maintain. If performance matters, you can even put the most likely occurrences towards the top of the list.

Reaching for semantics
On a semantic level, what you are checking for is set membership. However, you implement it on a very low level, basically inlining all the code needed to achieve the check. Apart from forcing the reader to infer the intent behind that massive condition, a prominent issue with such an approach is the large number of degrees of freedom in a general Boolean expression: to be sure the whole thing amounts to just checking set membership, one must carefully inspect each clause, minding any parentheses, misspellings of the repeated variable name, and more.
Each loose degree of freedom means exposure to not just one more bug, but to one more class of bugs.
An approach which uses an explicit set would have these advantages:
clear and explicit semantics;
tight constraint on the degrees of freedom to look after;
O(1) time complexity vs. O(n) complexity of your code.
This is the code needed to implement a set-based idiom:
static final Set<String> matches =
unmodifiableSet(new HashSet<>(asList("a","b","c")));
...
if (matches.contains(a)) // do something;
*I'm implying import static java.util.Arrays.asList and import static java.util.Collections.unmodifiableSet

Readability Is Mostly Formatting
Not readable...
if(a.equals("x") || a.equals("y") || a.equals("z") || Any number of terms...... )
//Do something
Now easy to real...
if(a.equals("x") ||
a.equals("y") ||
a.equals("z") ||
Any number of terms...... )
//Do something
Readability is very subjective to the person reading the source code.
If I came across code that implements collections, loops or one of the many other complicated answers here. I'd shake my head in disbelieve.
Separate The Logic From The Problem
You are mixing two different things. There is the problem of making the business logic easy to read, and the problem of implementing the business logic.
if(validState(a))
// Do something
How you implement validState doesn't matter. What's important is that code with the if statement is readable as business logic. It should not be a long chain of Boolean operations that hide the intent of what is happening.
Here is an example of readable business logic.
if(!isCreditCard(a)) {
return false;
}
if(isExpired(a)) {
return false;
}
return paymentAuthorized(a);
At some level there has to be code that processes basic logic, strings, arrays, etc.. etc.. but it shouldn't be at this level.
If you find you often have to check if a string is equal to a bunch of other strings. Put that code into a string utility class. Separate it from your work and keep your code readable. By ensuring it shows what you're really trying to do.

You can use Arrays.asList().This is the simplest approach and less verbosity.
Arrays.asList("x","y","z"...).contains(a)
For performance reason if your collection is too big you could put data in a HashSet cause searching there is in constant time.
Example make your own util method
public final class Utils{
private Utils(){}//don't let instantiate
public static <T> boolean contains(T a,T ... x){
return new HashSet<>(Arrays.asList(x)).contains(a);
}
}
Then in your client code:
if(Utils.contains(a,"x","y","z","n")){
//execute some code
}

With a little bit of help, you can get the syntactic sugar of a nicer if-statement with just a tiny bit of overhead. To elaborate on Tim's recommendation and Jesko's recommendation a tad further...
public abstract class Criteria {
public boolean matchesAny( Object... objects ) {
for( int i = 0, count = objects.length; i < count; i++ ) {
Object object = objects[i];
if( matches( object ) ) {
return true;
}
}
return false;
}
public boolean matchesAll( Object... objects ) {
for( int i = 0, count = objects.length; i < count; i++ ) {
Object object = objects[i];
if( !matches( object ) ) {
return false;
}
}
return true;
}
public abstract boolean matches( Object object );
}
public class Identity extends Criteria {
public static Identity of( Object self ) {
return new Identity( self );
}
private final Object self;
public Identity( Object self ) {
this.self = self;
}
#Override
public boolean matches( Object object ) {
return self != null ? self.equals( object ) : object == null;
}
}
Your if-statement would then look like this:
if( Identity.of( a ).matchesAny( "x", "y", "z" ) ) {
...
}
This is sort of a middle ground between having a generic syntax for this sort of conditional matching and having the expression describe a specific intent. Following this pattern also lets you perform the same sort of matching using criteria other than equality, much like how Comparators are designed.
Even with the improved syntax, this conditional expression is still just a little bit too complex. Further refactoring might lead to externalizing the terms "x", "y", "z" and moving the expression into a method whose name clearly defines its intent:
private static final String [] IMPORTANT_TERMS = {
"x",
"y",
"z"
};
public boolean isImportant( String term ) {
return Identity.of( term ).matchesAny( IMPORTANT_TERMS );
}
...and your original if-statement would finally be reduced to...
if( isImportant( a ) ) {
...
}
That's much better, and now the method containing your conditional expression can more readily focus on Doing One Thing.

Independent of what you are trying to achieve, this
if(a.equals("x") || a.equals("y") || a.equals("z") || Any number of terms...... )
//Do something
is always messy and unclean. In the first place it is just too long to make sense of it quickly.
The simplest solution for me would be to express your intend instead of being explicit.
Try to do this instead:
public class SomeClass{
public void SomeMethod(){
if ( matchesSignificantChar(a) ){
//doSomething
}
}
private bool matchesSignificantChar(String s){
return (s.equals("x") || s.equals("y") || s.equals("z") || Any number of terms...... )
}
}
This simplifies the scope of your conditional statement and makes it easier to understand while moving the complexity to a much smaller and named scope, that is headed by your intend.
However, this is still not very extensible. If you try to make it cleaner, you can extract the boolean method into another class and pass it as a delegate to SomeClass'es Constructor or even to SomeMethod. Also you can look into the Strategy Pattern for even more exensiblity.
Keep in mind that as a programmer you will spend much more time reading code (not only yours) than writing it, so creating better understandable code will pay off in the long run.

I use following pattern
boolean cond = false; // Name this variable reasonably
cond = cond || a.equals("x");
cond = cond || a.equals("y");
cond = cond || a.equals("z");
// Any number of terms......
if (cond) {
// ...
}
Note: no objects created on the heap. Also you can use any conditions, not only "equals".
In ruby you can use operator ||= for this purpose like cond ||= a.equals("x").

The Set answer is good. When not comparing for membership of a collection you can also separate out some or all of the conditional statement into methods. For example
if (inBounds(x) && shouldProcess(x) ) {
}

If a is guaranteed to be of length 1, you could do:
if ("xyz".indexOf(a) != -1)

One really nice way to do something like this is to use ASCII values, assuming your actual case here is where a is a char or a single character string. Convert a to its ASCII integer equivalent, then use something like this:
If you want to check that a is either "t", "u", "v", ... , "z", then do.....
If (val >= 116 && val <= 122) {//code here}

I prefer to use regexp like few guys wrote upper.
But also you can use next code
private boolean isOneMoreEquals(Object arg, Object... conditions) {
if (conditions == null || arg == null) {
return false;
}
for (int i = 0, d = conditions.length; i < d; i++) {
if (arg.equals(conditions[i])) {
return true;
}
}
return false;
}
so your code will be next:
if (isOneMoreEquals(a, "x", "y", "z") {
//do something
}

Assuming that your "x", "y", and "z" can be of arbitrary length, you can use
if (0 <= java.util.Arrays.binarySearch(new String[] { "x", "y", "z" }, a)) {
// Do something
}
Just make sure that you list your items in lexicographic order, as required by binarySearch(). That should be compatible all the way back to Java 1.2, and it should be more efficient than the solutions that use Java Collections.
Of course, if your "x", "y", and "z" are all single characters, and a is also a character, you can use if (0 <= "xyz".indexOf(a)) { ... } or
switch (a) {
case 'x': case 'y': case 'z':
// Do something
}

If x,y,z... is Consecutive， you can use if(a >= 'x' && a <= '...'), if not, you can use ArrayList or just Arrays.

I think that cleanest and fastest way is to put values in array.
String[] values={"value1","value2","value3"};
for (string value : values) {
if (a.equals(value){
//Some code
}
}