利用jdk1.8的stream，让你的代码上升一个层次

约定不等于承诺〃 2022-01-22 14:37 136阅读 0赞

文章公众号连接：[https://mp.weixin.qq.com/s/m5Knf35LFH5DZEiqUsUMqw][https_mp.weixin.qq.com_s_m5Knf35LFH5DZEiqUsUMqw]

# 简介 #

jdk1.8新增了一个接口类stream，和我们之前接触的字节流概念不一样，stream相当于高级版的Iterator，可以通过lambada表达式对集合就行各种遍历高效的聚合操作，或者大批量的数据操作。  
stream：数据串行操作  
parallelStream：并行操作，在多核cpu下优势明显

# 使用 #

## forEach循环数据 ##

### 示例地址 ###

[https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/ForeachSample.java][https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_ForeachSample.java]

### 示例说明 ###

循环输出list对象里面的每一个属性

### 示例代码 ###

public static void main(String[] args) {
    		List<Test> list = init();
    		list.stream().forEach(test->{
    			System.out.println(test.getAge());
    			System.out.println(test.getName());
    		});
    	}

## sorted排序 ##

### 示例地址 ###

[https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/SortedSamples.java][https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_SortedSamples.java]

### 示例说明 ###

根据年龄排序

### 示例代码 ###

:: 意思是映射Test类下的getAge方法

public static void main(String[] args) {
    		List<Test> list = init();
    		list.stream().sorted(Comparator.comparing(Test :: getAge)).forEach(test->{
    			System.out.println(test.getAge());
    			System.out.println(test.getName());
    		});
    	}

## filter过滤 ##

### 示例地址 ###

[https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/FilterSample.java][https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_FilterSample.java]

### 示例说明 ###

条件过滤，输出年龄大于5的数据

### 示例代码 ###

public static void main(String[] args) {
    		List<Test> list = init();
    		list.stream().filter((Test test)->test.getAge()>5).forEach(test->{
    			System.out.println(test.getAge());
    			System.out.println(test.getName());
    		});
    	}

## limit截断 ##

### 示例地址 ###

[https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/LimitSample.java][https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_LimitSample.java]

### 示例说明 ###

输出前5条数据

### 示例代码 ###

public static void main(String[] args) {
    		List<Test> list = init();
    		list.stream().limit(5).forEach(test->{
    			System.out.println(test.getAge());
    			System.out.println(test.getName());
    		});
    	}

## skip跳过 ##

### 示例地址 ###

[https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/SkipSample.java][https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_SkipSample.java]

### 示例说明 ###

跳过前五条数据

### 示例代码 ###

public static void main(String[] args) {
    		List<Test> list = init();
    		list.stream().skip(5).forEach(test->{
    			System.out.println(test.getAge());
    			System.out.println(test.getName());
    		});
    	}

## distinct 去重 ##

### 示例地址 ###

[https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/DistinctSample.java][https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_DistinctSample.java]

### 示例说明 ###

去除重复的数据

### 示例代码 ###

public static void main(String[] args) {
    		List<Test> list = init();
    		list.stream().distinct().forEach(test->{
    			System.out.println(test.getAge());
    			System.out.println(test.getName());
    		});
    	}

## 基础数据统计 ##

### 示例地址 ###

[https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/StatisticsSample.java][https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_StatisticsSample.java]

### 示例说明 ###

获取总共人数、平均年龄、最大年龄、最小年龄、年龄之和

### 示例代码 ###

public static void main(String[] args) {
    		List<Test> list = init();
    		IntSummaryStatistics statics = list.stream().mapToInt(test->test.getAge()).summaryStatistics();
    		System.out.println("总共人数：" + statics.getCount());
    	    System.out.println("平均年龄：" + statics.getAverage());
    	    System.out.println("最大年龄：" + statics.getMax());
    	    System.out.println("最小年龄：" + statics.getMin());
    	    System.out.println("年龄之和：" + statics.getSum());
    	}

[https_mp.weixin.qq.com_s_m5Knf35LFH5DZEiqUsUMqw]: https://mp.weixin.qq.com/s/m5Knf35LFH5DZEiqUsUMqw
[https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_ForeachSample.java]: https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/ForeachSample.java
[https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_SortedSamples.java]: https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/SortedSamples.java
[https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_FilterSample.java]: https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/FilterSample.java
[https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_LimitSample.java]: https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/LimitSample.java
[https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_SkipSample.java]: https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/SkipSample.java
[https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_DistinctSample.java]: https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/DistinctSample.java
[https_github.com_itrickzhang_stream-demo-1_blob_master_src_main_java_com_example_demo_examples_StatisticsSample.java]: https://github.com/itrickzhang/stream-demo-1/blob/master/src/main/java/com/example/demo/examples/StatisticsSample.java