Java Stream How to - Map Object on one attribute, then filter and count

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Question

We would like to know how to map Object on one attribute, then filter and count.

Answer

import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
//from   w  w  w  . jav a2  s.c  o  m
public class Main {

  public static void main(String[] args) {
    List<Trade> trades = TradeUtil.createTrades();

    Function<Trade, Integer> doubledQty = t -> {
        t.setQuantity(t.getQuantity() * 2); 
        return t.getQuantity();
    };
    
    long x = trades.stream()
            .map(doubledQty)
            .filter(qty -> qty > 15)
            .count();

    System.out.println(x);

  }

}

class TradeUtil {

  public static List<Trade> createTrades() {
    List<Trade> trades = new ArrayList<Trade>();

    Trade t = new Trade(1, "IBM", 10, "NEW");
    trades.add(t);
    t = new Trade(2, "APPL", 20, "PENDING");
    trades.add(t);
    t = new Trade(3, "IBM", 30, "NEW");
    trades.add(t);
    t = new Trade(4, "IBM", 40, "PENDING");
    trades.add(t);

    return trades;
  }

  public static List<Trade> createTrades(int size) {
    List<Trade> trades = new ArrayList<>();

    for (int i = 0; i < size; i++) {
      Trade t = new Trade(i, "ISUER " + i, i + 1000, "NEW");
      trades.add(t);
    }
    return trades;
  }
}

class Trade {

  private int tradeId = 0;
  private String issuer = null;
  private int quantity = 0;
  private String status = null;

  public Trade(int id, String issuer, int quantity, String status) {
    this.tradeId = id;
    this.issuer = issuer;
    this.quantity = quantity;
    this.status = status;
  }

  public int getTradeId() {
    return tradeId;
  }

  public void setTradeId(int tradeId) {
    this.tradeId = tradeId;
  }

  public String getIssuer() {
    return issuer;
  }

  public void setIssuer(String issuer) {
    this.issuer = issuer;
  }

  public int getQuantity() {
    return quantity;
  }

  public void setQuantity(int quantity) {
    this.quantity = quantity;
  }

  public String getStatus() {
    return status;
  }

  public void setStatus(String status) {
    this.status = status;
  }

  @Override
  public String toString() {
    return "Trade{" + "tradeId=" + tradeId + ", issuer=" + issuer
        + ", quantity=" + quantity + ", status=" + status + '}';
  }

}

The code above generates the following result.

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