Java8 新特性之 Function总结

桃扇骨 2024-02-05 19:30 63阅读 0赞

**目录**

Function< T , R >

DoubleFunction< R >

DoubleToIntFunction

DoubleToLongFunction

IntFunction < R >

IntToDoubleFunction

IntToLongFunction

LongFunction < R >

LongToDoubleFunction

LongToIntFunction

ToDoubleBiFunction < T , U >

ToDoubleFunction < T >

ToIntBiFunction < T , U >

ToIntFunction < T >

ToLongBiFunction < T , U >

ToLongFunction < T >

Java8 Function实例

--------------------

[函数式接口][Link 1](Functional Interface)就是一个有且仅有一个抽象方法，但是可以有多个非抽象方法的接口。且用@Function标签标记的接口。

[Java8][] 新增加的函数接口在 java.util.function 包下，它包含了很多类，用来支持 Java 的函数式编程，该包中的函数式接口有：

### Function< T , R > ###

函数产生给定数据类型的结果，并接受一个参数作为给定数据类型,`T`参数类型,`R`是结果类型。

public static void functionExamp(){
        
    		Function<Integer, String> message = age -> "年龄：".concat(String.valueOf(age));
    		System.out.print(message.apply(18));
    	}

### DoubleFunction< R > ###

只接收`double`数据类型的值，并以给定的数据类型返回结果

public static void doubleFunctionExample(){
        
    		// 四舍五入转换int
    		DoubleFunction<Integer> message = paramte  -> (int)Math.round(paramte);
    		System.out.println(message.apply(18.56));
    	}

### DoubleToIntFunction ###

接收`double`数据类型的值，并以`integer`数据类型返回结果。

public static void doubleToIntFunctionExample(){
        
    		DoubleToIntFunction message = f -> new Double(f).intValue();
    		System.out.println(message.applyAsInt(19.23));
    	}

### DoubleToLongFunction ###

接收`double`数据类型的值，并以`long`数据类型返回结果。

public static void doubleToLongFunctionExample(){
        
    		DoubleToLongFunction message = f -> new Double(f).longValue();
    		System.out.println(message.applyAsLong(19.23));
    	}

### IntFunction < R > ###

只接收`integer`数据类型的值，并以给定的数据类型返回结果。

public static void intFunctionExample(){
        
    		IntFunction<String> message = paramter -> String.valueOf(paramter);
    		System.out.println(message.apply(10));
    	}

### IntToDoubleFunction ###

接收`integer`数据类型的值，并以`double`数据类型返回结果。

public static void intToDoubleFunctionExample(){
        
    		IntToDoubleFunction message = paramter -> paramter * 2.3;
    		System.out.println(message.applyAsDouble(10));
    	}

### IntToLongFunction ###

接收`integer`数据类型的值，并以`long`数据类型返回结果。

public static void intToLongFunctionExample(){
        
        	IntToLongFunction message = paramter -> paramter;
        	System.out.println(message.applyAsLong(10));
        }

### LongFunction < R > ###

只接收`long`数据类型的值，并以给定的数据类型返回结果。

public static void longFunctionExample(){
        
        	LongFunction<Integer> message = paramter -> new Long(paramter).intValue();
        	System.out.println(message.apply(10));
        }

### LongToDoubleFunction ###

接收`long`数据类型的值，并以`double`数据类型返回结果。

public static void longToDoubleExample(){
        
        	LongToDoubleFunction message = paramter -> paramter * paramter;
        	System.out.println(message.applyAsDouble(123));
        }

### LongToIntFunction ###

接收`integer`数据类型的值，并以`integer`数据类型返回结果。

public static void longToIntExample(){
        
        	// 类型强制转换
        	LongToIntFunction message = paramter -> (int)paramter;
        	System.out.println(message.applyAsInt(23));
        }

### ToDoubleBiFunction < T , U > ###

接收给定数据类型的两个参数，并产生`double`数据类型的结果。

public static void toDoubleBitFunctionExample(){
        
        	ToDoubleBiFunction<Integer, Integer> message = (k1, k2) -> k1 + k2;
        	System.out.println(message.applyAsDouble(23, 12345));
        }

### ToDoubleFunction < T > ###

接收给定数据类型的值并产生`double`数据类型的结果。

public static void toDoubleFunctionExample(){
        
        	ToDoubleFunction<String> message = paramter -> Double.valueOf(paramter);
        	System.out.println(message.applyAsDouble("11.23"));
        }

### ToIntBiFunction < T , U > ###

接收两个给定数据类型的参数，产生`integer`数据类型的结果。

public static void toIntBitFuctionExample(){
        
        	 ToIntBiFunction<Integer,Integer> message = (f1,f2) -> f1+f2;
        	 System.out.println(message.applyAsInt(1, 2));
        }

### ToIntFunction < T > ###

接收一个给定数据类型的参数并产生`integer`数据类型的结果。

public static void toIntFunctionExample(){
        
        	ToIntFunction<String> convert = paramter -> Integer.valueOf(paramter);
        	System.out.println(convert.applyAsInt("123456"));
        }

### ToLongBiFunction < T , U > ###

接收两个给定数据类型的参数，产生`long`数据类型的结果。

public static void toLongBitFunctionExample(){
        
        	 ToLongBiFunction<Double,Integer> convert = (f1,f2) -> f1.intValue() + f2;
        	 System.out.println(convert.applyAsLong(23.45, 10));
        }

### ToLongFunction < T > ###

接收一个给定数据类型的参数并产生`long`数据类型的结果。

public static void toLongFunctionExample(){
        
        	DecimalFormat df = new DecimalFormat("0.00");//保留两位小数点
        	 ToLongFunction<String> convert = paramter -> Long.valueOf(paramter);
        	 System.out.println(df.format(convert.applyAsLong("11")));
        }

### Java8 Function实例 ###

package com.digipower.test;
     
    import java.text.DecimalFormat;
    import java.util.function.DoubleFunction;
    import java.util.function.DoubleToIntFunction;
    import java.util.function.DoubleToLongFunction;
    import java.util.function.Function;
    import java.util.function.IntFunction;
    import java.util.function.IntToDoubleFunction;
    import java.util.function.IntToLongFunction;
    import java.util.function.LongFunction;
    import java.util.function.LongToDoubleFunction;
    import java.util.function.LongToIntFunction;
    import java.util.function.ToDoubleBiFunction;
    import java.util.function.ToDoubleFunction;
    import java.util.function.ToIntBiFunction;
    import java.util.function.ToIntFunction;
    import java.util.function.ToLongBiFunction;
    import java.util.function.ToLongFunction;
     
    public class FunctionTest {
        
    	
    	public static void functionExamp(){
        
    		Function<Integer, String> message = age -> "年龄：".concat(String.valueOf(age));
    		System.out.println(message.apply(18));
    	}
    	
    	public static void doubleFunctionExample(){
        
    		// 四舍五入转换int
    		DoubleFunction<Integer> message = paramte  -> (int)Math.round(paramte);
    		System.out.println(message.apply(18.56));
    	}
    	
    	public static void doubleToIntFunctionExample(){
        
    		DoubleToIntFunction message = f -> new Double(f).intValue();
    		System.out.println(message.applyAsInt(19.23));
    	}
    	
    	public static void doubleToLongFunctionExample(){
        
    		DoubleToLongFunction message = f -> new Double(f).longValue();
    		System.out.println(message.applyAsLong(19.23));
    	}
    	
    	public static void intFunctionExample(){
        
    		IntFunction<String> message = paramter -> String.valueOf(paramter);
    		System.out.println(message.apply(10));
    	}
    	
    	public static void intToDoubleFunctionExample(){
        
    		IntToDoubleFunction message = paramter -> paramter * 2.3;
    		System.out.println(message.applyAsDouble(10));
    	}
    	
        public static void intToLongFunctionExample(){
        
        	IntToLongFunction message = paramter -> paramter;
        	System.out.println(message.applyAsLong(10));
        }
        
        public static void longFunctionExample(){
        
        	LongFunction<Integer> message = paramter -> new Long(paramter).intValue();
        	System.out.println(message.apply(10));
        }
        
        public static void longToDoubleExample(){
        
        	LongToDoubleFunction message = paramter -> paramter * paramter;
        	System.out.println(message.applyAsDouble(123));
        }
        
        public static void longToIntExample(){
        
        	// 类型强制转换
        	LongToIntFunction message = paramter -> (int)paramter;
        	System.out.println(message.applyAsInt(23));
        }
        
        public static void toDoubleBitFunctionExample(){
        
        	ToDoubleBiFunction<Integer, Integer> message = (k1, k2) -> k1 + k2;
        	System.out.println(message.applyAsDouble(23, 12345));
        }
        
        public static void toDoubleFunctionExample(){
        
        	ToDoubleFunction<String> message = paramter -> Double.valueOf(paramter);
        	System.out.println(message.applyAsDouble("11.23"));
        }
        
        public static void toIntBitFuctionExample(){
        
        	 ToIntBiFunction<Integer,Integer> message = (f1,f2) -> f1+f2;
        	 System.out.println(message.applyAsInt(1, 2));
        }
        
        public static void toIntFunctionExample(){
        
        	ToIntFunction<String> convert = paramter -> Integer.valueOf(paramter);
        	System.out.println(convert.applyAsInt("123456"));
        }
        
        public static void toLongBitFunctionExample(){
        
        	 ToLongBiFunction<Double,Integer> convert = (f1,f2) -> f1.intValue() + f2;
        	 System.out.println(convert.applyAsLong(23.45, 10));
        }
        
        public static void toLongFunctionExample(){
        
        	DecimalFormat df = new DecimalFormat("0.00");//保留两位小数点
        	 ToLongFunction<String> convert = paramter -> Long.valueOf(paramter);
        	 System.out.println(df.format(convert.applyAsLong("11")));
        }
    	public static void main(String[] args) {
        
    		
    		// TODO Auto-generated method stub
    		functionExamp();
    		doubleFunctionExample();
    		doubleToIntFunctionExample();
    		doubleToLongFunctionExample();
    		intFunctionExample();
    		intToDoubleFunctionExample();
    		intToLongFunctionExample();
    		longFunctionExample();
    		longToDoubleExample();
    		longToIntExample();
    		toDoubleBitFunctionExample();
    		toDoubleFunctionExample();
    		toIntBitFuctionExample();
    		toIntFunctionExample();
    		toLongBitFunctionExample();
    		toLongFunctionExample();
    	}
     
    }

**效果截图**

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT_size_19_color_FFFFFF_t_70_g_se_x_16][]

更多Java8 Function函数，请参考：[https://www.runoob.com/java/java8-functional-interfaces.html][https_www.runoob.com_java_java8-functional-interfaces.html]

[Link 1]: https://so.csdn.net/so/search?q=%E5%87%BD%E6%95%B0%E5%BC%8F%E6%8E%A5%E5%8F%A3&spm=1001.2101.3001.7020
[Java8]: https://so.csdn.net/so/search?q=Java8&spm=1001.2101.3001.7020
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT_size_19_color_FFFFFF_t_70_g_se_x_16]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/7bc6b14afb904bca9f42fd6b77a28a40.png
[https_www.runoob.com_java_java8-functional-interfaces.html]: https://www.runoob.com/java/java8-functional-interfaces.html