Stream - Stream常用操作

傷城~ 2023-09-29 14:08 14阅读 0赞

package com.example.demoleetcode.demostream;
    
    import com.example.demoleetcode.demostring.User;
    import org.junit.jupiter.api.Test;
    
    import java.util.ArrayList;
    import java.util.List;
    import java.util.concurrent.atomic.AtomicBoolean;
    import java.util.stream.Collectors;
    
    import static java.lang.System.out;
    
    public class StreamTest {
        
        private List<User> plist = new ArrayList<>();
        private List<User> plist1 = new ArrayList<>();
        private List<List<User>> plistlist = new ArrayList<>();
    
        /**
         * 初始化数据方便测试
         */
        private void initData() {
        
            plist.add(new User(1, "舟山",22));
            plist.add(new User(2, "张三",24));
            plist.add(new User(3, "中山",22));
            plist.add(new User(4, "专生",29));
            plist.add(new User(5, "这是",21));
    
            plist1.add(new User(11, "舟山1",22));
            plist1.add(new User(21, "张三",23));
            plist1.add(new User(31, "中山1",22));
            plist1.add(new User(41, "专生1",29));
            plist1.add(new User(51, "这是1",21));
    
            plistlist.add(plist);
            plistlist.add(plist1);
        }
    
        /**
         * 只要name为张三的user
         */
        @Test
        public void testStreamSimpleFilter() {
        
            initData();
            //plist = plist.stream().filter(item -> "张三".equals(item.getName())).collect(Collectors.toList());
            plist = plist.stream().filter(item -> 24 == item.getAge() && "张三".equals(item.getName())).collect(Collectors.toList());
            plist.stream().forEach(item -> out.println(item.getId() + ":" + item.getName() + ":" + item.getAge()));
        }
    
        /**
         * 只要list里面有name为张三的user list（有一个就返回true）
         * @throws Exception
         */
        @Test
        public void testStreamAnyMatch() {
        
            initData();
            plistlist = plistlist.stream().filter(plist -> {
        
                AtomicBoolean found = new AtomicBoolean(false);
                plist.stream().anyMatch(temp -> {
        
                    if (temp.getName().equals("张三")) {
        
                        found.set(true);
                    }
                    return found.get();
                });
                return found.get();
            }).collect(Collectors.toList());
            plistlist.stream().forEach(item -> item.forEach( itemTemp -> out.println(itemTemp.getId() + ":" + itemTemp.getName() + ":" + itemTemp.getAge())));
        }
    
        /**
         * 同一个对象的多个条件
         * @throws Exception
         */
        @Test
        public void testStreamTwoFilter() {
        
            initData();
            plistlist = plistlist.stream().filter(
                    item -> {
        
                        AtomicBoolean flag1 = new AtomicBoolean(false);
                        AtomicBoolean flag2 = new AtomicBoolean(false);
                        item.stream().anyMatch(itemTemp -> {
        
                                    if (itemTemp.getName().equals("张三")) {
        
                                        flag1.set(true);
                                    }
                                    if (itemTemp.getAge() == 24) {
        
                                        flag2.set(true);
                                    }
                                    // 兼容后期的多条件 || &&
                                    return flag1.get() && flag2.get();
                                }
                        );
                        return flag1.get() && flag2.get();
                    }).collect(Collectors.toList());
            plistlist.stream().forEach(item -> item.forEach( itemTemp -> out.println(itemTemp.getId() + ":" + itemTemp.getName() + ":" + itemTemp.getAge())));
        }
        /**
        * 排序测试
        */
    	@Test
        public void testStreamSortedList() {
        
            initData();
             plist = plist.stream().sorted(comparing(User::getAge).reversed()).collect(Collectors.toList());
            plist.stream().forEach(itemTemp -> out.println(itemTemp.getId() + ":" + itemTemp.getName() + ":" + itemTemp.getAge()));
        }
    
    
    
    }