Array - Java

• Basic
  • Collection of similar data type elements
• Commands
  • int var[]; => Declaring an Array
  • int var[n]; => Declaring an Array of size "n"
  • int[] var; => Declaring an Array
  • int[] var = {val1, val2, val3}; => Initializing an Integer Array, We use this method when we already know the elements of the Array
  • int[] var = new int[n]; => Initializing an Integer Array of size "n"
  • var[n]; => Returns the value at that Index
  • var[n] = val; => Assign a value at that Index
  • var.length; => Returns length of Array, It is a property of a Array not a Function
  • Array.sort(var); => Sorts the Array in ascending order using sort Function from Array Class
  • Initializing an 2D Integer Array

      int[][] var = {{val1, val2, val3}, {val4, val5, val6}
    

  • var[n1][n2]; => Accessing value of 2D Array

ArrayList

• Basic
  • Like Array but of Dynamic nature
• Commands
  • Initialize an ArrayList of Integer

      ArrayList<Integer> var = new ArrayList<Integer>();
    

  • Initialize an ArrayList of String

      ArrayList<String> var = new ArrayList<String>();
    

  • Initialize an ArrayList of Integer with values

      ArrayList<Integer> var = new ArrayList<Integer>(Array.asList(val1, val2, val3));
    

  • var[n] = val => Insert a value
  • var.size(); => Returns length of Array
  • var.add(val) => Insert the given value at the end
  • var.add(n, val) => Insert the value at index "n"
  • var.sort(Comparator.naturalOrder()) => Sorts the Array in ascending order
  • var.sort(Comparator.reverseOrder()) => Sorts the Array in descending order
  • System.out.println(var) => Print all elements of ArrayList