Question

How to check if ArrayList has duplicate strings in Java

Answer 1

package javaapplication1;

import java.util.ArrayList;

public class JavaApplication1 {

    public static boolean HasDuplicates(ArrayList<String> list) {
        for (int i = 0; i < list.size(); i++) {
            for (int j = i + 1; j < list.size(); j++) {
                if (list.get(i) == list.get(j)) {
                    return true;
                }
            }
        }
        return false;
    }

    public static void main(String[] args) {

        try {

            ArrayList<String> list = new ArrayList<>();
            list.add("java");
            list.add("c");
            list.add("c++");
            list.add("java");

            if (HasDuplicates(list)) {
                System.out.println("yes");
            } else {
                System.out.println("no");
            }

            list.removeIf(s -> s == "java");

            if (HasDuplicates(list)) {
                System.out.println("yes");
            } else {
                System.out.println("no");
            }

        } catch (Exception e) {
            System.out.println(e.toString());
        }
    }
}

/*
                  
run:
     
yes
no
         
 */

 

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Answer 2

package javaapplication1;

import java.util.ArrayList;

public class JavaApplication1 {

    public static boolean HasDuplicates(ArrayList<String> list) {
        for (int i = 0; i < list.size(); i++) {
            for (int j = i + 1; j < list.size(); j++) {
                if (list.get(i).equals(list.get(j))) {
                    return true;
                }
            }
        }
        return false;
    }

    public static void main(String[] args) {

        try {

            ArrayList<String> list = new ArrayList<>();
            list.add("java");
            list.add("c");
            list.add("c++");
            list.add("java");

            if (HasDuplicates(list)) {
                System.out.println("yes");
            } else {
                System.out.println("no");
            }

            list.removeIf(s -> "java".equals(s));

            if (HasDuplicates(list)) {
                System.out.println("yes");
            } else {
                System.out.println("no");
            }

        } catch (Exception e) {
            System.out.println(e.toString());
        }
    }
}

/*
                  
run:
     
yes
no
         
 */

 

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Answer 3

package javaapplication1;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;

public class JavaApplication1 {

    public static void main(String[] args) {

        try {

            ArrayList<String> list = new ArrayList<>();
            list.add("java");
            list.add("c");
            list.add("c++");
            list.add("java");

            Set<String> set = new HashSet<String>(list);
         
           if(set.size() < list.size()) {
                System.out.println("yes");
            } else {
                System.out.println("no");
            }

            list.removeIf(s -> "java".equals(s));

            if(set.size() < list.size()) {
                System.out.println("yes");
            } else {
                System.out.println("no");
            }

        } catch (Exception e) {
            System.out.println(e.toString());
        }
    }
}

/*
                  
run:
     
yes
no
         
 */

 

70+ SQL courses for beginners and professionals