java新特性-lambda表达式&方法引用&streamApi

  1 public class MethodRefTest {
  2 
  3     /**
  4      * 情况一：对象 :: 实例方法
  5      */
  6     //Consumer中的void accept(T t)
  7     //PrintStream中的void println(T t)
  8     @Test
  9     public void test1() {
 10         Consumer<String> con1 = str -> System.out.println(str);
 11         con1.accept("北京");
 12 
 13         PrintStream ps = System.out;
 14         Consumer<String> con2 = ps::println;
 15         con2.accept("beijing");
 16     }
 17     
 18     //Supplier中的T get()
 19     //Employee中的String getName()
 20     @Test
 21     public void test2() {
 22         Employee emp = new Employee(1001,"Tom",23,5600);
 23         // 匿名内部类
 24         Supplier<String> sup1 = new Supplier<String>() {
 25             @Override
 26             public String get() {
 27                 return emp.getName();
 28             }
 29         };
 30         // lambda
 31         Supplier<String> sup2 = () -> emp.getName();
 32         // 方法引用
 33         Supplier<String> sup3 = emp::getName;
 34 
 35         System.out.println(sup1.get());
 36         System.out.println(sup2.get());
 37         System.out.println(sup3.get());
 38     }
 39 
 40     /**
 41      * 情况二：类 :: 静态方法
 42      */
 43     //Comparator中的int compare(T t1,T t2)
 44     //Integer中的int compare(T t1,T t2)
 45     @Test
 46     public void test3() {
 47         // 匿名内部类
 48         Comparator<Integer> com1 = new Comparator<Integer>() {
 49             @Override
 50             public int compare(Integer o1, Integer o2) {
 51                 return Integer.compare(o1,o2);
 52             }
 53         };
 54         // lambda
 55         Comparator<Integer> com2 = (t1,t2) -> Integer.compare(t1,t2);
 56         // 方法引用
 57         Comparator<Integer> com3 = Integer::compare;
 58 
 59         System.out.println(com1.compare(12,21));
 60         System.out.println(com2.compare(12,3));
 61         System.out.println(com3.compare(12,12));
 62 
 63     }
 64     
 65     //Function中的R apply(T t)
 66     //Math中的Long round(Double d)
 67     @Test
 68     public void test4() {
 69         // 匿名内部类
 70         Function<Double,Long> func1 = new Function<Double, Long>() {
 71             @Override
 72             public Long apply(Double d) {
 73                 return Math.round(d);
 74             }
 75         };
 76         // lambda
 77         Function<Double,Long> func2 = d -> Math.round(d);
 78         // 方法引用
 79         Function<Double,Long> func3 = Math::round;
 80 
 81         System.out.println(func1.apply(12.6));
 82         System.out.println(func2.apply(12.6));
 83         System.out.println(func3.apply(12.6));
 84     }
 85 
 86     /**
 87      * 情况三：类 :: 实例方法  (有难度)
 88      * 如下：参数1作为调用者，参数2作为方法参数
 89      */
 90 
 91     // Comparator中的int comapre(T t1,T t2)
 92     // String中的int t1.compareTo(t2)
 93     @Test
 94     public void test5() {
 95         // 匿名内部类
 96         Comparator<String> com1 = new Comparator<String>() {
 97             @Override
 98             public int compare(String o1, String o2) {
 99                 return o1.compareTo(o2);
100             }
101         };
102         // lambda
103         Comparator<String> com2 = (s1,s2) -> s1.compareTo(s2);
104         // 方法引用
105         Comparator<String> com3 = String :: compareTo;
106 
107         System.out.println(com1.compare("abd","abm"));
108         System.out.println(com2.compare("abd","abm"));
109         System.out.println(com3.compare("abd","abm"));
110     }
111 
112     //BiPredicate中的boolean test(T t1, T t2);
113     //String中的boolean t1.equals(t2)
114     @Test
115     public void test6() {
116         // 匿名内部类
117         BiPredicate<String,String> pre1 = new BiPredicate<String, String>() {
118             @Override
119             public boolean test(String s1, String s2) {
120                 return s1.equals(s2);
121             }
122         };
123         // lambda
124         BiPredicate<String,String> pre2 = (s1,s2) -> s1.equals(s2);
125         // 方法引用
126         BiPredicate<String,String> pre3 = String :: equals;
127 
128         System.out.println(pre1.test("abc","abd"));
129         System.out.println(pre2.test("abc","abd"));
130         System.out.println(pre3.test("abc","abd"));
131     }
132     
133     // Function中的R apply(T t)    如下：t就是employee
134     // Employee中的String t.getName();
135     @Test
136     public void test7() {
137         Employee employee = new Employee(1001, "Jerry", 23, 6000);
138 
139         // 匿名内部类
140         Function<Employee,String> func1 = new Function<Employee, String>() {
141             @Override
142             public String apply(Employee employee) {
143                 return employee.getName();
144             }
145         };
146         // lambda
147         Function<Employee,String> func2 = e -> e.getName();
148         // 方法引用
149         Function<Employee,String> func3 = Employee::getName;
150 
151         System.out.println(func1.apply(employee));
152         System.out.println(func2.apply(employee));
153         System.out.println(func3.apply(employee));
154     }
155 }