Java Stream How to - Collect one attribute and save into a list

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Question

We would like to know how to collect one attribute and save into a list.

Answer

/*  w  w  w.j  av a 2  s.  c  om*/
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class Main {

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

    List<Integer> list = trades.stream()
            .map(t->t.getQuantity())
            .collect(Collectors.toList());
    System.out.println("Collect List: "+list);
  }

}
class TradeUtil {

  public static List<Trade> createTrades(){
      List<Trade> trades = new ArrayList<Trade>();
      
      Trade t = new Trade(1,"IBM",1000,"NEW");
      trades.add(t);
      t = new Trade(2,"APPL",2000,"NEW");
      trades.add(t);
      t = new Trade(3,"IBM",3000,"NEW");
      trades.add(t);
      t = new Trade(4,"IBM",4000,"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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