[英]ArrayList counting equal objects
我有一個名為class的產品。 此類中的所有字段都是從數據庫填充的:
public class Product {
private Long id;
private String code;
private String name;
private String type;
private Integer quantity;
private Integer numOfPieces;
private Integer sumOfPieces;
private String savingPeriod;
private Double costPrice;
private Double price;
public Product() {
}
public Product(Long id, String code, String name, String type, Integer
quantity, Integer numOfPieces, Integer sumOfPieces, String savingPeriod,
Double costPrice, Double price) {
this.id = id;
this.code = code;
this.name = name;
this.type = type;
this.quantity = quantity;
this.numOfPieces = numOfPieces;
this.sumOfPieces = sumOfPieces;
this.savingPeriod = savingPeriod;
this.costPrice = costPrice;
this.price = price;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
public Integer getQuantity() {
return quantity;
}
public void setQuantity(Integer quantity) {
this.quantity = quantity;
}
public Integer getNumOfPieces() {
return numOfPieces;
}
public void setNumOfPieces(Integer numOfPieces) {
this.numOfPieces = numOfPieces;
}
public Integer getSumOfPieces() {
return sumOfPieces;
}
public void setSumOfPieces(Integer sumOfPieces) {
this.sumOfPieces = sumOfPieces;
}
public String getSavingPeriod() {
return savingPeriod;
}
public void setSavingPeriod(String savingPeriod) {
this.savingPeriod = savingPeriod;
}
public Double getCostPrice() {
return costPrice;
}
public void setCostPrice(Double costPrice) {
this.costPrice = costPrice;
}
public Double getPrice() {
return price;
}
public void setPrice(Double price) {
this.price = price;
}
@Override
public String toString() {
return "Product{" + "id=" + id + ", code=" + code + ", name=" + name + ", type=" + type + ", quantity=" + quantity + ", numOfPieces=" + numOfPieces + ", sumOfPieces=" + sumOfPieces + ", savingPeriod=" + savingPeriod + ", costPrice=" + costPrice + ", tax=" + price + '}';
}
@Override
public int hashCode() {
int hash = 7;
hash = 83 * hash + Objects.hashCode(this.id);
hash = 83 * hash + Objects.hashCode(this.code);
hash = 83 * hash + Objects.hashCode(this.name);
hash = 83 * hash + Objects.hashCode(this.type);
hash = 83 * hash + Objects.hashCode(this.quantity);
hash = 83 * hash + Objects.hashCode(this.numOfPieces);
hash = 83 * hash + Objects.hashCode(this.sumOfPieces);
hash = 83 * hash + Objects.hashCode(this.savingPeriod);
hash = 83 * hash + Objects.hashCode(this.costPrice);
hash = 83 * hash + Objects.hashCode(this.price);
return hash;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final Product other = (Product) obj;
if (!Objects.equals(this.code, other.code)) {
return false;
}
if (!Objects.equals(this.name, other.name)) {
return false;
}
if (!Objects.equals(this.type, other.type)) {
return false;
}
if (!Objects.equals(this.savingPeriod, other.savingPeriod)) {
return false;
}
if (!Objects.equals(this.id, other.id)) {
return false;
}
if (!Objects.equals(this.quantity, other.quantity)) {
return false;
}
if (!Objects.equals(this.numOfPieces, other.numOfPieces)) {
return false;
}
if (!Objects.equals(this.sumOfPieces, other.sumOfPieces)) {
return false;
}
if (!Objects.equals(this.costPrice, other.costPrice)) {
return false;
}
if (!Objects.equals(this.price, other.price)) {
return false;
}
return true;
}
}
我有一個ProductsController類可與數據庫一起使用:
ProductsController productsController = new ProductsController();
我創建一個新的ArrayList並添加一些具有相同信息的產品對象:
Product p1 = productsController.findOneById(1); //p1.getName() = "Analgin"
Product p2 = productsController.findOneById(1); //p2.getName() = "Analgin"
Product p3 = productsController.findOneById(1); //p3.getName() = "Analgin"
Product p4 = productsController.findOneById(1); //p4.getName() = "Analgin"
Product p5 = productsController.findOneById(2); //p5.getName() = "Pikovid"
Product p6 = productsController.findOneById(2); //p6.getName() = "Pikovid"
Product p7 = productsController.findOneById(3); //p7.getName() = "Bolnol"
List<Product> productsList = new ArrayList<>();
如何為以下輸出計算ArrayList中的相同元素:
Javlonbek,
我建議您使用Java Streams的“ groupingBy”功能。
productsList.stream().collect(
Collectors.groupingBy(product -> product.getName(),
Collectors.counting())
);
在您的示例中,輸出按頻率降序排列。 我不確定這是意外還是故意的。 streamApi還允許您進行排序。 參見mkyong網站上的示例[1]。
干杯,馬可
1: https : //www.mkyong.com/java8/java-8-collectors-groupingby-and-mapping-example/
我看到您已經實現了equals和hashCode,因此足以構建一個像這樣的映射:
HashMap <String, Product> productsByName = new HashMap <>();
productsByName.put(product1.getName(), product1);
productsByName.put(product2.getName(), product2);
// add all the products
並且此映射已經包含了此類信息,足以通過給定名稱查詢產品列表,例如:
List <Product> analginProducts = productsByName.get("Analgin");
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