JDK1.8新接口Predicate<T>及Function初步使用

本文代码改自：http://www.concretepage.com/java/jdk-8/java-8-predicate-example

JDK1.8支持lambda expression，使用方式与传统写法差别不小。见代码：

package collection.myInterface;import java.util.Date;import java.util.function.Function;public class Start {    public int length;    public String name;    public Date finddata;    public Start() {        length = 1;        name = "fq";        finddata = new Date();    }    public Start(int length, String name, Date finddata){        this.length = length;        this.name = name;        this.finddata = finddata;    }    public int getLength() {        return length;    }    public void setLength(int length) {        this.length = length;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Date getFinddata() {        return finddata;    }    public void setFinddata(Date finddata) {        this.finddata = finddata;    }    public String show(Function<Start, String> func){        System.out.println("======I'm Function.apply======"+func.apply(this));        return "显示信息： length="+this.length+";name="+this.name+";Date="+finddata;    }}

这是调用：

package collection.myInterface;import java.util.function.Function;import java.util.function.Predicate;public class Client {    public static void main(String[] args) {        Predicate<Start> malestart = abs -> abs.length >= 20 && "male".equals(abs.name);        Predicate<Start> femalestart = abs -> abs.length > 15 && "female".equals(abs.name);        Function<Start, String> maleStyle = abs -> "Hi, You are male and length " + abs.length;        Function<Start, String> femaleStyle = abs -> "Hi, You are female and length " + abs.length;//      Start s1 = new Start(20, "male", null);        Start s1 = new Start(20, "female", null);        if (malestart.test(s1)) {            System.out.println(s1.show(maleStyle));            /*             ======I'm Function.apply======Hi, You are male and length 20              显示信息： length=20;name=male;Date=null             */        } else if (femalestart.test(s1)) {            System.out.println(s1.show(femaleStyle));        }    }}

重点：

- 验证方式

Predicate < Start > malestart = abs -> abs.length >= 20 &&
“male”.equals(abs.name);

此处Start是刚刚我自定义的类型，而abs就是这个类型的形参，以这个符号（->）做为后面验证条件的赋值。并把这种验证称做“malestart”验证。转换成传统Java写法是这样：
Boolean malestart(Start abs){
return abs.length >= 20 && “male”.equals(abs.name);
}

- 定义function

Function < Start, String > maleStyle = abs -> “Hi, You are male and
length ” + abs.length;

Funtionrg后面的<>，第一个参数是入参类型，第二个是出参类型，maleStyle是函数名，(->)之后的是Function具体方法。转义成Java的写法是
String maleStyle(Start abs){
return “Hi, You are male and length ” + abs.length;
}

- 使用方法：

Start s1 = new Start(20, “female”, null); //这是要加验证的对象 if
(malestart.test(s1)) { … }

– 这里就是对s1调用malestart验证了，会返回boolean。

• 程序执行结果
  ======I’m Function.apply======Hi, You are female and length 20
  显示信息： length=20;name=female;Date=null

一看show方法便知，不叨

Function和Predicate的其它方法写API：
http://docs.oracle.com/javase/8/docs/api/java/util/function/Function.html
http://docs.oracle.com/javase/8/docs/api/java/util/function/Predicate.html