private static class LongCache {
 private LongCache(){}

 static final Long cache[] = new Long[-(-128) + 127 + 1];

 static {
   for(int i = 0; i < cache.length; i++)
 cache[i] = new Long(i - 128);
 }
  }

public class Test05 {

  public static void main(String[] args) {
    Long a = 5L;
    Long b = 5L;

    System.out.println("a == b ? " + (a == b));

    Long c = 129L;
    Long d = 129L;
    System.out.println("c == d ? " + (c == d));
  }
}

a == b ? true
c == d ? false

public class Test06 {
  Long l = 3L;
}

{
java.lang.Long l;

public com.spring.test.Test06();
 Code:
  Stack=3, Locals=1, Args_size=1
  0:  aload_0
  1:  invokespecial  #10; //Method java/lang/Object."<init>":()V
  4:  aload_0
  5:  ldc2_w #12; //long 3l
  8:  invokestatic  #14; //Method java/lang/Long.valueOf:(J)Ljava/lang/Long;
  11: putfield    #20; //Field l:Ljava/lang/Long;
  14: return
 LineNumberTable:
  line 3: 0
  line 5: 4
  line 3: 14

 LocalVariableTable:
  Start Length Slot Name  Signature
  0   15   0  this    Lcom/spring/test/Test06;


}

 public static Long valueOf(long l) {
 final int offset = 128;
 if (l >= -128 && l <= 127) { // will cache
   return LongCache.cache[(int)l + offset];
 }
    return new Long(l);
  }

public boolean equals(Object obj) {
 if (obj instanceof Long) {
   return value == ((Long)obj).longValue();
 }
 return false;
  }