要获取AWS实例的公共IP地址，可以使用AWS SDK for Java。以下是一个使用AWS SDK for Java获取AWS EC2实例公共IP地址的示例代码：

首先，确保已经在项目中导入了AWS SDK for Java的依赖。

import com.amazonaws.auth.AWSStaticCredentialsProvider;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.ec2.AmazonEC2;
import com.amazonaws.services.ec2.AmazonEC2ClientBuilder;
import com.amazonaws.services.ec2.model.DescribeInstancesRequest;
import com.amazonaws.services.ec2.model.DescribeInstancesResult;
import com.amazonaws.services.ec2.model.Instance;

public class GetPublicIP {

    public static void main(String[] args) {
        // 认证信息
        BasicAWSCredentials awsCreds = new BasicAWSCredentials("ACCESS_KEY", "SECRET_KEY");

        // 创建AmazonEC2客户端
        AmazonEC2 ec2Client = AmazonEC2ClientBuilder.standard()
                .withCredentials(new AWSStaticCredentialsProvider(awsCreds))
                .withRegion("REGION")
                .build();

        // 创建DescribeInstancesRequest请求
        DescribeInstancesRequest request = new DescribeInstancesRequest();

        // 发送请求并获取结果
        DescribeInstancesResult result = ec2Client.describeInstances(request);

        // 遍历每个实例并打印公共IP地址
        for (Reservation reservation : result.getReservations()) {
            for (Instance instance : reservation.getInstances()) {
                String publicIp = instance.getPublicIpAddress();
                System.out.println("Instance ID: " + instance.getInstanceId());
                System.out.println("Public IP: " + publicIp);
            }
        }
    }
}

在上面的代码中，你需要将ACCESS_KEY和SECRET_KEY替换为你的AWS访问密钥。同时，将REGION替换为你希望操作的AWS区域。

通过上述代码，你可以获取到每个EC2实例的公共IP地址。