內容目錄

Supplier in Java with Examples

只有一個抽象方法的接口，定義了 get 方法，可以在一個元素上測試或應用一些操作，常用於建立預設值，例如：當物件為 Null 時，傳回預設值，取代傳統實作接口的方法，讓程式碼更加簡潔和易讀， Supplier in Java 本篇增加了範例，並透過單元測試來驗證產出結果。

@FunctionalInterface
public interface Supplier<T> {
    T get();
}

檔案目錄

./
   +- src
       +- test
       |   +- org
       |       +- ruoxue
       |           +- java_147
       |               +- functional
       |                   +- supplier
       |                        +- SupplierWithExamplesTest.java

單元測試

Supplier Java 提供 get 等操作 Supplier 。

Food

建立 Food 類別，覆寫 equals 、 hashCode ，定義屬性和方法，用來建立一個物件。

	@NoArgsConstructor
	@Getter
	@Setter
	@Builder
	public static class Food {
		private String name;
		private double quantity;
		private int type;

		public Food(String name, double quantity, int type) {
			this.name = name;
			this.quantity = quantity;
			this.type = type;
		}

		public String toString() {
			ToStringBuilder builder = new ToStringBuilder(this, ToStringStyle.JSON_STYLE);
			builder.appendSuper(super.toString());
			builder.append("name", name);
			builder.append("quantity", quantity);
			builder.append("type", type);
			return builder.toString();
		}

		public boolean equals(Object object) {
			if (!(object instanceof Food)) {
				return false;
			}
			if (this == object) {
				return true;
			}
			Food other = (Food) object;
			return new EqualsBuilder().append(getName(), other.getName()).isEquals();
		}

		public int hashCode() {
			return new HashCodeBuilder().append(getName()).toHashCode();
		}
	}

get

建立 Supplier 物件，操作 get 方法，取得物件。

	@Test
	public void get() {
		Supplier<Food> value = () -> new Food("Bacon", 1, 1);
		Food result = value.get();
		System.out.println(result);
		assertNotNull(result);
		value = () -> new Food("Ham", 2, 1);
		result = value.get();
		System.out.println(result);
		assertNotNull(result);
		value = () -> new Food("Pork", 3, 1);
		result = value.get();
		System.out.println(result);
		assertNotNull(result);
	}

{"name":"Bacon","quantity":1.0,"type":1}
{"name":"Ham","quantity":2.0,"type":1}
{"name":"Pork","quantity":3.0,"type":1}

traditional

Java Supplier 使用傳統方式，實作 Supplier 接口，取得物件。

	public static class DefaultValue<E> implements Supplier<Food> {
		@Override
		public Food get() {
			return new Food("DEFAULT_FOOD", 1, 1);
		}
	}

	@Test
	public void traditional() {
		DefaultValue<Food> defaultValue = new DefaultValue<Food>();
		Food result = defaultValue.get();
		System.out.println(result);
		assertNotNull(result);
	}

{"name":"DEFAULT_FOOD","quantity":1.0,"type":1}

SupplierWithExamplesTest.java

Supplier in Java 新增單元測試，驗證 Java Supplier Example 是否符合預期。

package org.ruoxue.java_147.functional;

import static org.junit.Assert.*;

import java.util.function.Supplier;
import org.apache.commons.lang3.builder.EqualsBuilder;
import org.apache.commons.lang3.builder.HashCodeBuilder;
import org.apache.commons.lang3.builder.ToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;
import org.junit.Test;

import lombok.Builder;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;

public class SupplierWithExamplesTest {

	@NoArgsConstructor
	@Getter
	@Setter
	@Builder
	public static class Food {
		private String name;
		private double quantity;
		private int type;

		public Food(String name, double quantity, int type) {
			this.name = name;
			this.quantity = quantity;
			this.type = type;
		}

		public String toString() {
			ToStringBuilder builder = new ToStringBuilder(this, ToStringStyle.JSON_STYLE);
			builder.appendSuper(super.toString());
			builder.append("name", name);
			builder.append("quantity", quantity);
			builder.append("type", type);
			return builder.toString();
		}

		public boolean equals(Object object) {
			if (!(object instanceof Food)) {
				return false;
			}
			if (this == object) {
				return true;
			}
			Food other = (Food) object;
			return new EqualsBuilder().append(getName(), other.getName()).isEquals();
		}

		public int hashCode() {
			return new HashCodeBuilder().append(getName()).toHashCode();
		}
	}

	@Test
	public void get() {
		Supplier<Food> value = () -> new Food("Bacon", 1, 1);
		Food result = value.get();
		System.out.println(result);
		assertNotNull(result);
		value = () -> new Food("Ham", 2, 1);
		result = value.get();
		System.out.println(result);
		assertNotNull(result);
		value = () -> new Food("Pork", 3, 1);
		result = value.get();
		System.out.println(result);
		assertNotNull(result);
	}

	public static class DefaultValue<E> implements Supplier<Food> {
		@Override
		public Food get() {
			return new Food("DEFAULT_FOOD", 1, 1);
		}
	}

	@Test
	public void traditional() {
		DefaultValue<Food> defaultValue = new DefaultValue<Food>();
		Food result = defaultValue.get();
		System.out.println(result);
		assertNotNull(result);
	}
}