Generic types in Java -

is right code

list<integer> test2 = new arraylist<integer>(); test2.add(343); int x2 = test2.get(0); 

in compile time converted this

list test = new arraylist(); test.add(343); int x = (integer)test.get(0); 

something similar autoboxing...

let's try. take class 2 methods absolutely same thing , without generics , autoboxing:

public class generictest{      // use generics , auto-boxing     // java 1.5 or higher required     public void generic(){         final list<integer> test2 = new arraylist<integer>();         test2.add(343);         final int x2 = test2.get(0);     }      // use neither generics nor auto-boxing,     // should java 1.4-compatible     public void nongeneric(){         final list test2 = new arraylist();         test2.add(integer.valueof(343));         final int x2 = ((integer) test2.get(0)).intvalue();     } } 

here's byte code:

// compiled generictest.java (version 1.6 : 50.0, super bit) public class generictest {    // method descriptor #6 ()v   // stack: 1, locals: 1   public generictest();     0  aload_0 [this]     1  invokespecial java.lang.object() [8]     4  return       line numbers:         [pc: 0, line: 4]       local variable table:         [pc: 0, pc: 5] local: index: 0 type: generictest    // method descriptor #6 ()v   // stack: 2, locals: 3   public void generic();      0  new java.util.arraylist [16]      3  dup      4  invokespecial java.util.arraylist() [18]      7  astore_1 [test2]      8  aload_1 [test2]      9  sipush 343     12  invokestatic java.lang.integer.valueof(int) : java.lang.integer [19]     15  invokeinterface java.util.list.add(java.lang.object) : boolean [25] [nargs: 2]     20  pop     21  aload_1 [test2]     22  iconst_0     23  invokeinterface java.util.list.get(int) : java.lang.object [31] [nargs: 2]     28  checkcast java.lang.integer [20]     31  invokevirtual java.lang.integer.intvalue() : int [35]     34  istore_2 [x2]     35  return       line numbers:         [pc: 0, line: 7]         [pc: 8, line: 8]         [pc: 21, line: 9]         [pc: 35, line: 10]       local variable table:         [pc: 0, pc: 36] local: index: 0 type: generictest         [pc: 8, pc: 36] local: test2 index: 1 type: java.util.list         [pc: 35, pc: 36] local: x2 index: 2 type: int       local variable type table:         [pc: 8, pc: 36] local: test2 index: 1 type: java.util.list<java.lang.integer>    // method descriptor #6 ()v   // stack: 2, locals: 3   public void nongeneric();      0  new java.util.arraylist [16]      3  dup      4  invokespecial java.util.arraylist() [18]      7  astore_1 [test2]      8  aload_1 [test2]      9  sipush 343     12  invokestatic java.lang.integer.valueof(int) : java.lang.integer [19]     15  invokeinterface java.util.list.add(java.lang.object) : boolean [25] [nargs: 2]     20  pop     21  aload_1 [test2]     22  iconst_0     23  invokeinterface java.util.list.get(int) : java.lang.object [31] [nargs: 2]     28  checkcast java.lang.integer [20]     31  invokevirtual java.lang.integer.intvalue() : int [35]     34  istore_2 [x2]     35  return       line numbers:         [pc: 0, line: 13]         [pc: 8, line: 14]         [pc: 21, line: 15]         [pc: 35, line: 16]       local variable table:         [pc: 0, pc: 36] local: index: 0 type: generictest         [pc: 8, pc: 36] local: test2 index: 1 type: java.util.list         [pc: 35, pc: 36] local: x2 index: 2 type: int } 

i don't see obvious difference between generic , non-generic version, in fact here's diff result 2 methods:

<  public void generic(); --- >   public void nongeneric(); 19,22c19,22 <         [pc: 0, line: 7] <         [pc: 8, line: 8] <         [pc: 21, line: 9] <         [pc: 35, line: 10] --- >         [pc: 0, line: 13] >         [pc: 8, line: 14] >         [pc: 21, line: 15] >         [pc: 35, line: 16] 27,28d26 <       local variable type table: <         [pc: 8, pc: 36] local: test2 index: 1 type: java.util.list<java.lang.integer> 

as can see, difference in line numbers , local variable table.