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Static import In java

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instanceof java

Posts: 576
Nickname: instanceof
Registered: Jan, 2015

instanceof java is a java related one.
Static import In java Posted: Mar 31, 2015 6:47 AM
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  • If we want to reuse any predefined class or user defined class or interface or enum which is present in a package we need to import those  entire packages or those classes so that we can use those classes present inside the package.

  • import packagename.ClassTest;
  • import packagename.*;
  • For example if we want to read some data from keyboard we can use scanner class present in util package.
  • import java.util.Scanner;
  • We can import everything inside a package by using .*
  • import java.util.*;
  • Without importing want to use that class then code seems to like this




  1. package com.instanceofjava;
  2. class A{
  3.   
  4. public static void main(String [] args){
  5.  
  6.    int number;
  7.   java.util.Scanner in = new java.util.Scanner(System.in);
  8.  
  9.     System.out.println("Enter a number to check even or odd");
  10.     number=in.nextInt();
  11.   
  12.  
  13. }
  14. }

  • if we use import no need to mention class name in declaration 


  1. package com.instanceofjava;
  2.  
  3. import java.util.Scanner;
  4.  
  5. class A{
  6.   
  7. public static void main(String [] args){
  8.  
  9.    int number;
  10.   Scanner in = new Scanner(System.in);
  11.  
  12.     System.out.println("Enter a number to check even or odd");
  13.     number=in.nextInt();
  14.   
  15.  
  16. }
  17. }


Static import:

  • Normal imports will import the all the classes so that we can use them. similarly static imports will import all static data so that can use without class name.
  • In JDk 1.5 these static imports introduced.
  • Lets see one program without static import.

 Without Static Import:


  1. package com.instanceofjava;
  2.  
  3. class StaticImport{
  4.   
  5. public static void main(String [] args){
  6.  
  7.     System.out.println(Math.PI); //3.141592653589793
  8.     System.out.println(Integer.MAX_VALUE);//2147483647
  9.     System.out.println(Integer.parseInt("123"));//123
  10.  
  11. }
  12. }

Using Static import:


  1. package com.instanceofjava;
  2.  
  3.  import static java.lang.Integer.*;
  4.  import static java.lang.Math.*;
  5.  
  6. class StaticImport{
  7.   
  8. public static void main(String [] args){
  9.  
  10.     System.out.println(PI); //3.141592653589793
  11.     System.out.println(MAX_VALUE);//2147483647
  12.     System.out.println(parseInt("123"));//123
  13.  
  14. }
  15. }


Importing Math class:

 

  1. package com.instanceofjava;
  2.  
  3.  import static java.lang.Math.*;
  4.  
  5. class StaticImport{
  6.   
  7. public static void main(String [] args){
  8.  
  9.     System.out.println(PI); //3.141592653589793

  11.     double square;
  12.  
  13.     double d1 = 3.0;
  14.     double   d2 = 4.0;
  15.  
  16.     square = sqrt(pow(d1, 2) + pow(d2, 2));
  17.     System.out.println(square);
  18.  
  19. }
  20. }

Importing System class:

 

  1. package com.instanceofjava;
  2.  
  3.  import static java.lang.System.out;
  4.  
  5. class StaticImport{
  6.   
  7. public static void main(String [] args){
  8.  
  9.      out.println("Good morning, " + "java2s");
  10.      out.println("Have a day!");
  11.  
  12. }
  13. }

Importing User defined classes:



  1. package com.instanceofjava;

  3.  
  4. class Colors{
  5.  
  6.      public static int white = 1;
  7.      public static int black = 2;
  8.      public static int red = 3;
  9.      public static int blue = 4;
  10.      public static int orange = 5;
  11.      public static int grey = 6;
  12.      public static int green =7;
  13.  
  14. }


  1. package com.instanceofjava;

  3.  import static com.instanceofjava.Colors.*; 

  5. class StaticImportDemo{
  6.  
  7. public static void main(String [] args){
  8.  
  9.     System.out.println(white );//1
  10.     System.out.println(blue);//4
  11.  
  12. }
  13.  
  14. }


Arrays and Collections:





  1. package com.instanceofjava;

  3.  import static com.instanceofjava.Colors.*; 

  5. class StaticImportDemo{
  6.  
  7. public static void main(String [] args){
  8.  
  9.    int[] array = new int[] {5, 4, 6, 3, 2, 1};
  10.  
  11.         sort(array);
  12.  
  13.      for (int i = 0; i < array.length; i++) {
  14.             System.out.print(array[i]+" ");
  15.       }  
  16.  
  17.   ArrayList al= new ArrayList();
  18.        al.add(1);
  19.         al.add(12);
  20.         al.add(3);
  21.        al.add(2);
  22.  
  23.        sort(al); 

  25.          Iterator itr= al.iterator();
  26.          while(itr.hasNext()){
  27.              System.out.printl(itr.next()+" ");
  28.          }
  29.  
  30. }
  31.  
  32. }

OutPut:

  1. 1 2 3 4 5 6
  2. 1 2 3 12

Advantages and Disadvantages of Static imports

  • One of the advantage of using static imports is reducing keystrokes and re usability.
  • System.out.println() ; we can write as out.println() .  But using eclipse short cut syso (ctrl+sapce)  gives System.out.println() faster than static imports usage. 
  • And there may be a chance of  complexity in readability.
  • If we use class name before method like Math.sqrt() then can understand easily that method belongs to particular class . with static imports reduces readability.
  • One more disadvantage is naming conflicts.
  • If we use Integer.Max_value we cannot use Float.Max_value

Read: Static import In java

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