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smolthing
smolthing

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Almost all the types in Java

#java

Java Data Types - group of objects

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Basic Examples 

// example.java import java.lang.Boolean; import java.lang.Double; import java.lang.Float; import java.lang.Integer; import java.lang.Long; import java.lang.String; import java.util.ArrayList; import java.util.HashMap; import java.util.HashSet; import java.util.LinkedList; import java.util.Map; import java.util.Set; public class Example { public static void main(String[] args) { // Primitive types byte myByte = 127; // 8-bit, 2^8, -128 to 127 short myShort = 32767; // 16-bit, 2^16. -32768 to 32767 int myInt = 2147483647; // 32-bit, 2^32, -2147483648 to -2147483647 long myLong = 9223372036854775807L; // 64-bit, 2^64, -9223372036854775808 to 9223372036854775807L, L otherwise float myFloat = 3.14f; // 32-bit, 2^32,  double myDouble = 3.141592653589793; // 64-bit, 2^64 char myChar = 'A'; // 16-bit, 2^16,  boolean myBoolean = true; // 1-bit, 2^1 // Reference types String myString = "Hello, world!"; Class myClass = String.class; Object myObject = new Object(); // Collection data types ArrayList<String> myArrayList = new ArrayList<>(); myArrayList.add("Apple"); myArrayList.add("Orange"); myArrayList.add("Banana"); LinkedList<String> myLinkedList = new LinkedList<>(); myLinkedList.add("Apple"); myLinkedList.add("Orange"); myLinkedList.add("Banana"); Set<String> mySet = new HashSet<>(); mySet.add("Apple"); mySet.add("Orange"); mySet.add("Banana"); Map<String, Integer> myMap = new HashMap<>(); myMap.put("Apple", 1); myMap.put("Orange", 2); myMap.put("Banana", 3); // Print out the result System.out.println("myByte: " + myByte); System.out.println("myShort: " + myShort); System.out.println("myInt: " + myInt); System.out.println("myLong: " + myLong); System.out.println("myFloat: " + myFloat); System.out.println("myDouble: " + myDouble); System.out.println("myChar: " + myChar); System.out.println("myBoolean: " + myBoolean); System.out.println("myString: " + myString); System.out.println("myClass: " + myClass); System.out.println("myObject: " + myObject); System.out.println("myArrayList: " + myArrayList); System.out.println("myLinkedList: " + myLinkedList); System.out.println("mySet: " + mySet); System.out.println("myMap: " + myMap); } }
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Results 

$ java ./example.java myByte: 127 myShort: 32767 myInt: 2147483647 myLong: 9223372036854775807 myFloat: 3.14 myDouble: 3.141592653589793 myChar: A myBoolean: true myString: Hello, world! myClass: class java.lang.String myObject: java.lang.Object@3745e5c6 myArrayList: [Apple, Orange, Banana] myLinkedList: [Apple, Orange, Banana] mySet: [Apple, Orange, Banana] myMap: {Apple=1, Orange=2, Banana=3}
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1. Set <-- HashSet

In 3Sum, we use hashset to improve lookup time for duplicate values.

... Set<List<Integer>> set = new HashSet<>(); set.add(Arrays.asList(1, 2, 3)); return new ArrayList<>(set); ...
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HashSet is a class that implements the Set interface in Java

Methods 

Set<List<Integer>> set = new HashSet<>(); // slow, less memory used HashSet<List<Integer>> set = new HashSet<>(); // fast, more memory
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Set = abstract class with basic functionality
HashSet = concrete class that implements Set interface

set.iteractor()/toArray()/add()/remove()/contains()/size()/isEmpty()
hashset.add()/remove()/contains()/size()/isEmpty()

Convert ArrayList to/from HashSet 

HashSet<String> hashSet = new HashSet<>(); hashSet.add("why so many types"); ArrayList<String> arrayList = new ArrayList<>(hashSet);
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HashSet<String> hashSet = new HashSet<>(); hashSet.add("help my brain"); ArrayList<String> arrayList = (ArrayList<String>) hashSet.toArray();
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Others

I will update them in the future. My brain is on max CPU at the moment.

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