Java-Array&ArrayList

• data[] a = new data[size] || data[]a = {*,* ,* ,* ,*… }(number of element = size)
  • declear and internalize a data type array named a
  • always internalize array
    • compiler error
  • data[][] a = new data[width][height] || data[][]a = {{*,*…},{* ,* …}{* ,*…}… }
    • two-dimension array
• a.length() return capacity of a
• copy array(data[] c = a) is share reference of data array to a and c
• length of array is fixed
  • can be repersented by a variable to avoid usage of magic number
• use Scanner.hasNextData and for loop to keep track number of element been internalized to Array
• for(data x : a) traverse all element been internalized into array
• use array iff you have a long list and known number of primitive data and can or should not convert to Wapper class

 

• use arrayList when you are not sure about how many element you will have
• import java.util.ArrayList package
  • a generic class(hold any data type)
• ArrayList<data> b = new ArrayList<data>();
  • declear and internalize
• useful functions
  • b.add(data1) add data1 to the end of b
  • b.add(n,data1) add data1 to the position n of b and the element after move 1 to the end
  • b.set(n,data1) set position n of b to data1
  • b.size() return number of element stored in b
  • b.get(n) get data stored at position n of b
  • b.remove(n) remove position n`s data, all data after go up 1
  • System.out.println(b) print all data stored in b as a string
• ArrayList <data> d = b || ArrayList<data> d = new ArrayList<data>(b)
  • copy reference of b to d
• 
• convert from primitive type to wrapper class is auto and use auto-boxing
• ArrayList can only use Wrapper class type not primitive type