//snippet-sourcedescription:[ListTopics.java demonstrates how to get a list of existing AWS SNS topics.]
//snippet-keyword:[Java]
//snippet-sourcesyntax:[java]
//snippet-keyword:[Code Sample]
//snippet-keyword:[Amazon Simple Notification Service]
//snippet-service:[sns]
//snippet-sourcetype:[full-example]
//snippet-sourcedate:[4/6/2020]
//snippet-sourceauthor:[scmacdon AWS]

/*
 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file is distributed
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package com.example.sns;

//snippet-start:[sns.java2.ListTopics.import]
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.sns.SnsClient;
import software.amazon.awssdk.services.sns.model.ListTopicsRequest;
import software.amazon.awssdk.services.sns.model.ListTopicsResponse;
import software.amazon.awssdk.services.sns.model.SnsException;
//snippet-end:[sns.java2.ListTopics.import]

public class ListTopics {
    public static void main(String[] args) {
        final String USAGE = "\n" +
                "ListTopics - returns a list of Amazon SNS topics.\n" +
                "Usage: ListTopics \n\n";


        SnsClient snsClient = SnsClient.builder()
                .region(Region.US_WEST_2)
                .build();

        listSNSTopics(snsClient);
    }

    //snippet-start:[sns.java2.ListTopics.main]
    public static void listSNSTopics(SnsClient snsClient) {

        try {
            ListTopicsRequest request = ListTopicsRequest.builder()
                    .build();

            ListTopicsResponse result = snsClient.listTopics(request);
            System.out.println("Status was " + result.sdkHttpResponse().statusCode() + "\n\nTopics\n\n" + result.topics());

    } catch (SnsException e) {

        System.err.println(e.awsErrorDetails().errorMessage());
        System.exit(1);
    }
        //snippet-end:[sns.java2.ListTopics.main]
    }
}

//snippet-sourcedescription:[ListTopics.java demonstrates how to get a list of existing Amazon SNS topics.]
//snippet-keyword:[Java]
//snippet-sourcesyntax:[java]
//snippet-keyword:[Code Sample]
//snippet-keyword:[Amazon Simple Notification Service]
//snippet-service:[sns]
//snippet-sourcetype:[full-example]
//snippet-sourcedate:[4/6/2020]
//snippet-sourceauthor:[scmacdon AWS]

/*
 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file is distributed
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package com.example.sns;

//snippet-start:[sns.java2.ListTopics.import]
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.sns.SnsClient;
import software.amazon.awssdk.services.sns.model.ListTopicsRequest;
import software.amazon.awssdk.services.sns.model.ListTopicsResponse;
import software.amazon.awssdk.services.sns.model.SnsException;
//snippet-end:[sns.java2.ListTopics.import]

public class ListTopics {
    public static void main(String[] args) {
        final String USAGE = "\n" +
                "ListTopics - returns a list of Amazon SNS topics.\n" +
                "Usage: ListTopics \n\n";


        SnsClient snsClient = SnsClient.builder()
                .region(Region.US_WEST_2)
                .build();

        listSNSTopics(snsClient);
    }

    //snippet-start:[sns.java2.ListTopics.main]
    public static void listSNSTopics(SnsClient snsClient) {

        try {
            ListTopicsRequest request = ListTopicsRequest.builder()
                    .build();

            ListTopicsResponse result = snsClient.listTopics(request);
            System.out.println("Status was " + result.sdkHttpResponse().statusCode() + "\n\nTopics\n\n" + result.topics());

    } catch (SnsException e) {

        System.err.println(e.awsErrorDetails().errorMessage());
        System.exit(1);
    }
        //snippet-end:[sns.java2.ListTopics.main]
    }
}

Update ListTopics.java