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BiPredicate in Java with Examples - Java 147

BiPredicate in Java with Examples – Java 147

BiPredicate in Java with Examples

只有一個抽象方法的接口，定義了 test 方法，可以在一個元素上測試或應用一些操作，常用於過濾條件，如：過濾數量介於 3 – 6 之間，取代傳統實作接口的方法，讓程式碼更加簡潔和易讀， BiPredicate 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 BiPredicate<T> {
    boolean test(T t, U u);
}

檔案目錄

./
   +- src
       +- test
       |   +- org
       |       +- ruoxue
       |           +- java_147
       |               +- functional
       |                   +- bipredicate
       |                       +- BiPredicateWithExamplesTest.java

單元測試

BiPredicate Java 提供 test 、 and 、 or 條件或組合成鏈式判斷等操作 BiPredicate 。

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();
		}
	}

test

建立 BiPredicate 物件，傳入 2 個參數，判斷是否為真。

	@Test
	public void test() {
		BiPredicate<Food, String> startsWith = (o, s) -> o.name.startsWith(s);
		Food food = new Food("Bacon", 1, 1);
		boolean result = startsWith.test(food, "B");
		System.out.println(result);
		assertTrue(result);
		food = new Food("Ham", 3, 1);
		result = startsWith.test(food, "B");
		System.out.println(result);
		assertFalse(result);
	}
true
false

negate

BiPredicate Java 建立 BiPredicate 物件，傳入 2 個參數，否定判斷。

	@Test
	public void negate() {
		BiPredicate<Food, String> startsWith = (o, s) -> o.name.startsWith(s);
		Food food = new Food("Bacon", 1, 1);
		boolean result = startsWith.negate().test(food, "B");
		System.out.println(result);
		assertFalse(result);
		food = new Food("Ham", 3, 1);
		result = startsWith.negate().test(food, "B");
		System.out.println(result);
		assertTrue(result);
	}
false
true

and

BiPredicate Java 建立 2 個 BiPredicate 物件，各傳入 2個參數，使用 and 組合判斷是否為真，並傳回 BiPredicate 是一個短路邏輯運算，其中當第一個 BiPredicate 為 False 時將不會評估第二個 BiPredicate 。

	@Test
	public void and() {
		BiPredicate<Food, String> startsWith = (o, s) -> o.name.startsWith(s);
		BiPredicate<Food, String> contains = (o, s) -> o.name.contains(s);
		Food food = new Food("Bacon", 1, 1);
		boolean result = startsWith.and(contains).test(food, "B");
		System.out.println(result);
		assertTrue(result);
		food = new Food("Ham", 3, 1);
		result = startsWith.and(contains).test(food, "B");
		System.out.println(result);
		assertFalse(result);
	}

true
false

or

BiPredicate Java 建立 2 個 BiPredicate 物件，各傳入 2 個參數，使用 or 組合判斷是否為真，並傳回 BiPredicate 是一個短路邏輯運算，其中當第一個 BiPredicate 為 True 時將不會評估第二個 BiPredicate 。

	@Test
	public void or() {
		BiPredicate<Food, String> startsWith = (o, s) -> o.name.startsWith(s);
		BiPredicate<Food, String> contains = (o, s) -> o.name.contains(s);
		Food food = new Food("Pork", 3, 1);
		boolean result = startsWith.or(contains).test(food, "o");
		System.out.println(result);
		assertTrue(result);
		result = startsWith.or(contains).test(food, "k");
		System.out.println(result);
		assertTrue(result);
	}

true
true

chaining

Java BiPredicate 建立多個 BiPredicate 物件，各傳入 2 個參數，使用 and 、 or 組合判斷是否為真。

	@Test
	public void chaining() {
		BiPredicate<Food, String> contains = (o, s) -> o.name.contains(s);
		BiPredicate<Food, String> startsWith = (o, s) -> o.name.startsWith(s);
		BiPredicate<Food, String> endsWith = (o, s) -> o.name.endsWith(s);
		Food food = new Food("BaconB", 1, 1);
		boolean result = contains.and(startsWith).or(endsWith).test(food, "B");
		System.out.println(result);
		assertTrue(result);
		food = new Food("Ham", 2, 1);
		result = contains.and(startsWith).or(endsWith).test(food, "B");
		System.out.println(result);
		assertFalse(result);
	}
true
false

traditional

Java BiPredicate 使用傳統方式，實作 BiPredicate 接口，判斷是否為真。

	public static class StartsWith<E> implements BiPredicate<Food, String> {
		@Override
		public boolean test(Food t, String u) {
			return t.name.startsWith(u);
		}
	}

	@Test
	public void traditional() {
		BiPredicate<Food, String> startsWith = new StartsWith<Food>();
		BiPredicate<Food, String> contains = (o, s) -> o.name.contains(s);
		Food food = new Food("Bacon", 1, 1);
		boolean result = startsWith.and(contains).test(food, "B");
		System.out.println(result);
		assertTrue(result);
		food = new Food("Ham", 2, 1);
		result = startsWith.and(contains).test(food, "B");
		System.out.println(result);
		assertFalse(result);
	}
true
false

BiPredicateWithExamplesTest.java

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

package org.ruoxue.java_147.functional.bipredicate;

import static org.junit.Assert.*;

import java.util.function.BiPredicate;
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 BiPredicateWithExamplesTest {

	@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 test() {
		BiPredicate<Food, String> startsWith = (o, s) -> o.name.startsWith(s);
		Food food = new Food("Bacon", 1, 1);
		boolean result = startsWith.test(food, "B");
		System.out.println(result);
		assertTrue(result);
		food = new Food("Ham", 3, 1);
		result = startsWith.test(food, "B");
		System.out.println(result);
		assertFalse(result);
	}

	@Test
	public void negate() {
		BiPredicate<Food, String> startsWith = (o, s) -> o.name.startsWith(s);
		Food food = new Food("Bacon", 1, 1);
		boolean result = startsWith.negate().test(food, "B");
		System.out.println(result);
		assertFalse(result);
		food = new Food("Ham", 3, 1);
		result = startsWith.negate().test(food, "B");
		System.out.println(result);
		assertTrue(result);
	}

	@Test
	public void and() {
		BiPredicate<Food, String> startsWith = (o, s) -> o.name.startsWith(s);
		BiPredicate<Food, String> contains = (o, s) -> o.name.contains(s);
		Food food = new Food("Bacon", 1, 1);
		boolean result = startsWith.and(contains).test(food, "B");
		System.out.println(result);
		assertTrue(result);
		food = new Food("Ham", 3, 1);
		result = startsWith.and(contains).test(food, "B");
		System.out.println(result);
		assertFalse(result);
	}

	@Test
	public void or() {
		BiPredicate<Food, String> startsWith = (o, s) -> o.name.startsWith(s);
		BiPredicate<Food, String> contains = (o, s) -> o.name.contains(s);
		Food food = new Food("Pork", 3, 1);
		boolean result = startsWith.or(contains).test(food, "o");
		System.out.println(result);
		assertTrue(result);
		result = startsWith.or(contains).test(food, "k");
		System.out.println(result);
		assertTrue(result);
	}

	@Test
	public void chaining() {
		BiPredicate<Food, String> contains = (o, s) -> o.name.contains(s);
		BiPredicate<Food, String> startsWith = (o, s) -> o.name.startsWith(s);
		BiPredicate<Food, String> endsWith = (o, s) -> o.name.endsWith(s);
		Food food = new Food("BaconB", 1, 1);
		boolean result = contains.and(startsWith).or(endsWith).test(food, "B");
		System.out.println(result);
		assertTrue(result);
		food = new Food("Ham", 2, 1);
		result = contains.and(startsWith).or(endsWith).test(food, "B");
		System.out.println(result);
		assertFalse(result);
	}

	public static class StartsWith<E> implements BiPredicate<Food, String> {
		@Override
		public boolean test(Food t, String u) {
			return t.name.startsWith(u);
		}
	}

	@Test
	public void traditional() {
		BiPredicate<Food, String> startsWith = new StartsWith<Food>();
		BiPredicate<Food, String> contains = (o, s) -> o.name.contains(s);
		Food food = new Food("Bacon", 1, 1);
		boolean result = startsWith.and(contains).test(food, "B");
		System.out.println(result);
		assertTrue(result);
		food = new Food("Ham", 2, 1);
		result = startsWith.and(contains).test(food, "B");
		System.out.println(result);
		assertFalse(result);
	}
}

心得分享

Java BiPredicate Example 功能接口，使用 Lambda 語法，可當作其他方法的傳入參數或是引用其他方法為實例， Java BiPredicate 提供了幾種 BiPredicate 常見方法的操作範例，例如： test 、 and 、 or 等方法。

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