Compare and Contains for Enum values and Get enum constant by name

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Compare and Contains for Enum values

Enums contains only constants and can be compared directly with ==. So, only reference check is needed, no need to use .equals method. Moreover, if .equals used incorrectly, may raise the NullPointerException while that's not the case with == check.

enum Day {
	GOOD, AVERAGE, WORST;
}
public class Test {
	public static void main(String[] args) {
		Day day = null;
		if (day.equals(Day.GOOD)) {//NullPointerException!
			System.out.println("Good Day!");
		}
		if (day == Day.GOOD) {//Always use == to compare enum
			System.out.println("Good Day!");
		}
	}
}

To group, complement, range the enum values we have EnumSet class which contains different methods.

• EnumSet#range : To get subset of enum by range defined by two endpoints
• EnumSet#of : Set of specific enums without any range. Multiple overloaded of methods are there.
• EnumSet#complementOf : Set of enum which is complement of enum values provided in method parameter

enum Page {
	A1, A2, A3, A4, A5, A6, A7, A8, A9, A10
}
 
public class Test {
	public static void main(String[] args) {
		EnumSet<Page> range = EnumSet.range(Page.A1, Page.A5);
 
		if (range.contains(Page.A4)) {
			System.out.println("Range contains A4");
		}
 
		EnumSet<Page> of = EnumSet.of(Page.A1, Page.A5, Page.A3);
 
		if (of.contains(Page.A1)) {
			System.out.println("Of contains A1");
		}
	}
}

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Get enum constant by name

Say we have an enum DayOfWeek:

enum DayOfWeek {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY;
}

An enum is compiled with a built-in static valueOf() method which can be used to lookup a constant by its name:

String dayName = DayOfWeek.SUNDAY.name();
assert dayName.equals("SUNDAY");
 
DayOfWeek day = DayOfWeek.valueOf(dayName);
assert day == DayOfWeek.SUNDAY;

This is also possible using a dynamic enum type:

Class<DayOfWeek> enumType = DayOfWeek.class;
DayOfWeek day = Enum.valueOf(enumType, "SUNDAY");
assert day == DayOfWeek.SUNDAY;

Both of these valueOf() methods will throw an IllegalArgumentException if the specified enum does not have a constant with a matching name.

The Guava library provides a helper method Enums.getIfPresent() that returns a Guava Optional to eliminate explicit exception handling:

DayOfWeek defaultDay = DayOfWeek.SUNDAY;
DayOfWeek day = Enums.valueOf(DayOfWeek.class, "INVALID").or(defaultDay);
assert day == DayOfWeek.SUNDAY;

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Enum with properties (fields)

In case we want to use enum with more information and not just as constant values, and we want to be able to compare two enums.

Consider the following example:

public enum Coin {
	PENNY(1), NICKEL(5), DIME(10), QUARTER(25);
 
	private final int value;
 
	Coin(int value){
		this.value = value;
	}
 
	public boolean isGreaterThan(Coin other){
		return this.value > other.value;
	}
}

Here we defined an Enum called Coin which represent its value. With the method isGreaterThan we can compare two enums:

Coin penny = Coin.PENNY;
Coin dime = Coin.DIME;
System.out.println(penny.isGreaterThan(dime)); // prints: false
System.out.println(dime.isGreaterThan(penny)); // prints: true

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Basic Programs

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• Creating Your First Java Program
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• Reference Data Types
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• Literals
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Strings in Java

• Comparing Strings
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StringBuffer and StringBuilder

• String Buffer
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Date Class

• Convert java.util.Date to java.sql.Date and Basic date
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• Comparing Date objects
• Converting String into Date and Time Zones and java.util.Date

Dates and Time (java.time.*)

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BigDecimal

• Comparing and Using BigDecimals
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BigInteger

• Initialization and Generating random BigIntegers
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Bit Manipulation

• Checking, setting, clearing, and toggling individual bits. Using long as bit mask
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Arrays

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Collections

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Enums

• Declaring and using a basic enum
• Enums with constructors and Abstract Methods
• Implements Interface and Singleton pattern
• Using methods and static blocks and Zero instance enum
• Enum constant specific body and Getting the values of an enum
• Compare and Contains for Enum values and Get enum constant by name
• Convert enum to String and Enums with static fields
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Properties Class

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Autoboxing

• Using int and Integer interchangeably and Auto-unboxing may lead to NullPointerException
• Different Cases When Integer and int can be used interchangeably

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