How to sort the arrays in ArrayList?

Question

I have ArrayList it contains so many arrays, each array contain first name, last name. now I want to sort the list based on the last name.

Example:

ArrayList<String[]> list=new ArrayList<String[]>();
 String[] name1={"koti" ,"reddy"};
 String[] name2={"hanu" ,"sanjay"};
 String[] name3={"ajay" ,"zedeja"};
 String[] name4={"basha" ,"kadhar"};
 list.add(name1);
 list.add(name2);
 list.add(name3);
 list.add(name4);

I want the sorting order like:

basha kadhar 
koti reddy 
hanu sanjay 
ajay zedeja 

Could you please help on this ASAP, Thanks in Advance

• Thai Tran: Check more about Collections docs.oracle.com/javase/6/docs/api/java/util/…

Answer 1

Write a custom Comparator and supply that to the appropriate sort overload along with the data.

However, I would recommend a separate Person/Name type, instead of String arrays, as it will make data easier to keep track of and it could implement Comparable (which would eliminate/replace the need of a Comparator).

Now, when writing an applicable compare/compareTo, the code should look similar to:

int cmpLastName = a_lastName.compareTo(b_lastName);
if (cmpLastName == 0) {
 // same lastname, order now based on first name
 return a_firstName.compareTo(b_firstName);
} else {
 // different lastname, so have enough ordering
 return cmpLastName;
}

Answer 2

try this

 Collections.sort(list, new Comparator<String[]>() {
 @Override
 public int compare(String[] o1, String[] o2) {
 int c = o1[0].compareTo(o2[0]);
 if (c != 0) {
 return c;
 }
 return o1[1].compareTo(o2[1]);
 }
 });

Answer 3

This is how I would perform that sort operation.

public static void main(String[] args) {
 ArrayList<String[]> list = new ArrayList<String[]>();
 String[] name1 = { "koti", "reddy" };
 String[] name2 = { "hanu", "sanjay" };
 String[] name3 = { "ajay", "zedeja" };
 String[] name4 = { "basha", "kadhar" };
 list.add(name1);
 list.add(name2);
 list.add(name3);
 list.add(name4);
 System.out.println("Before sorting");
 for (String[] r : list) {
 System.out.println(Arrays.toString(r));
 }
 Collections.sort(list, new Comparator<String[]>() {
 public int compare(String[] left, String[] right) {
 if (left == null) { // null?
 if (right == null) { // null == null!
 return 0;
 }
 return -1; // null < not(null)
 } else if (right == null) {
 return 1; // not(null) > null.
 }
 // If the last names aren't the same, return the result
 // of comparing the last names.
 if (left[1].compareTo(right[1]) != 0) {
 return left[1].compareTo(right[1]);
 }
 // Return the result of comparing the first names.
 return left[0].compareTo(right[0]);
 }
 });
 System.out.println("After sorting");
 for (String[] r : list) {
 System.out.println(Arrays.toString(r));
 }
}

Answer 4

try this code to achieve your output.

public static void main(String []args){
 ArrayList<String[]> list=new ArrayList<String[]>();
 String[] name1={"koti" ,"reddy"};
 String[] name2={"hanu" ,"sanjay"};
 String[] name3={"ajay" ,"zedeja"};
 String[] name4={"basha" ,"kadhar"};
 list.add(name1);
 list.add(name2);
 list.add(name3);
 list.add(name4);
 Collections.sort(list, new Comparator<String[]>() {
 @Override
 public int compare(String[] s1, String[] s2) {
 int i = s1[0].compareTo(s2[0]);
 if (i != 0) {
 return i;
 }
 return s1[1].compareTo(s2[1]);
 }
 });
 System.out.println("after sorting"+"\n");
 for (String[] s : list) {
 for(int i=0;i<s.length;i++){ 
 System.out.print(s[i]+"\t");
 }
 System.out.print("\n");
 }
}