Practice›Java Fundamentals›Module 5. Arrays & Lists›5.3 Lists

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5.3 Lists — sorting a list

Lesson

Не пишите сортировку сами

Java sorts a list for you: Collections.sort(list). It rearranges the list in place — it returns nothing, it changes the list you gave it.

Worked example

import java.util.Collections;

Collections.sort(names);   // names is now sorted
System.out.println(names);

Numbers go in increasing order, strings alphabetically — the same order compareTo gives. Note the import: Collections lives in java.util like ArrayList.

Careful with the common mistake names = Collections.sort(names); — the method returns nothing, so this does not compile.

▶ Try it: run this, then change something and run it again.

import java.util.ArrayList;
import java.util.Collections;

public class Main {
    public static void main(String[] args) {
        ArrayList<String> names = new ArrayList<String>();
        names.add("pear"); names.add("apple"); names.add("fig");
        Collections.sort(names);
        System.out.println(names);

        ArrayList<Integer> nums = new ArrayList<Integer>();
        nums.add(9); nums.add(2); nums.add(7);
        Collections.sort(nums);
        System.out.println(nums);
    }
}

Collections.sort(list)...

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Strings are sorted...

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Type exactly what this program prints.

import java.util.ArrayList;
import java.util.Collections;

public class Main { public static void main(String[] a){
    ArrayList<Integer> n = new ArrayList<Integer>();
    n.add(3); n.add(1); n.add(2);
    Collections.sort(n);
    System.out.println(n);
}}

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Why does list = Collections.sort(list); fail?

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True or false?

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