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import java.util.ArrayList;
public class TestWrapper1 {
 public static void main(String[] args) {
  //create an array list of integers, which each element
  //is more than 127
    ArrayList<Integer> list1 = new ArrayList<Integer>();
    for(int i=0;i<10;i++)
     list1.add(i+1000);
  //create another array list of integers, which each element
  //is the same with the first one
    ArrayList<Integer> list2 = new ArrayList<Integer>();
    for(int i=0;i<10;i++)
     list2.add(i+1000);   Â
       Â
    int counter = 0;
    for(int i=0;i<10;i++)
     if(list1.get(i) == list2.get(i)) counter++;
    //output the total equal number
    System.out.println(counter);
 }
}Â
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In JDK 51.6.0_10, the output of this code is 0. In this code, we want to count the same numbers of array list1 and array list2. Undoubtedly, the result are not the same as our expectation. But if we can set more caches inside Integer, then the result may be different!
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| Code Block |
|---|
public class TestWrapper1 {
 public static void main(String[] args) {
  //create an array list of integers, which each element
  //is more than 127
    ArrayList<Integer> list1 = new ArrayList<Integer>();
    for(int i=0;i<10;i++)
     list1.add(i+1000);
  //create another array list of integers, which each element
  //is the same with the first one
    ArrayList<Integer> list2 = new ArrayList<Integer>();
    for(int i=0;i<10;i++)
     list2.add(i+1000);   Â
       Â
    int counter = 0;
    for(int i=0;i<10;i++)
     if(list1.get(i).equals(list2.get(i))) counter++;
    //output the total equal number
    System.out.println(counter);
 }
}
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In JDK 1.6.0_10, the output of this code is 10.
Risk Assessment
We often use array list with primitive type, so it will exert a potential security risk.
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