Java 实现 List 中集合的元素进行排序

2022-11-12
浙江
本文字数：1958 字
阅读完需：约 6 分钟

简单集合排序

    public static List<Integer> getIntegerList(){        List<Integer> integerList = new ArrayList<>();        integerList.add(23);        integerList.add(15);        integerList.add(35);        integerList.add(68);        integerList.add(43);        integerList.add(8);        return integerList;    }
    /**     * Integer集合排序     */    @Test    public void sortIntegerList(){        List<Integer> integerList = getIntegerList();        System.out.println("排序前："+integerList);        //Integer本身有实现Comparable接口        Collections.sort(integerList);        System.out.println("排序后："+integerList);    }

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输出：

排序前：[23, 15, 35, 68, 43, 8]排序后：[8, 15, 23, 35, 43, 68]

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根据对象集合某个字段排序

    public static List<User> getUserList(){        List<User> userList = new ArrayList<>();        userList.add(new User("小明",11,"北京",66));        userList.add(new User("小红",12,"上海",99));        userList.add(new User("小詹",14,"广州",77));        userList.add(new User("小龙",16,"深圳",55));        userList.add(new User("小斯",9,"迈阿密",33));        userList.add(new User("小布",12,"伦敦",88));        return userList;    }
    @Test    public void sortUserListByAge(){        List<User> userList = getUserList();        System.out.println("排序前："+userList);        //如果想直接通过Collections.sort(userList)排序，需要User实现Comparable接口，并重写compareTo方法        Collections.sort(userList, new Comparator<User>() {            @Override            public int compare(User o1, User o2) {                //由小到大排序                return o1.getAge() - o2.getAge();                //由大到小排序                //return o2.getAge() - o1.getAge();            }        });        System.out.println("排序后："+userList);    }

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输出：

排序前：[User(name=小明, age=11, city=北京, score=66), User(name=小红, age=12, city=上海, score=99), User(name=小詹, age=14, city=广州, score=77), User(name=小龙, age=16, city=深圳, score=55), User(name=小斯, age=9, city=迈阿密, score=33), User(name=小布, age=12, city=伦敦, score=88)]排序后：[User(name=小斯, age=9, city=迈阿密, score=33), User(name=小明, age=11, city=北京, score=66), User(name=小红, age=12, city=上海, score=99), User(name=小布, age=12, city=伦敦, score=88), User(name=小詹, age=14, city=广州, score=77), User(name=小龙, age=16, city=深圳, score=55)]

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根据对象集合多个字段排序

    @Test    public void sortUserList(){        List<User> userList = getUserList();        System.out.println("排序前："+userList);        //如果想直接通过Collections.sort(userList)排序，需要User实现Comparable接口，并重写compareTo方法        Collections.sort(userList, new Comparator<User>() {            @Override            public int compare(User o1, User o2) {                //先按照年龄排序                int i = o1.getAge() - o2.getAge();                if(i == 0){                    //如果年龄相等再用分数进行排序                    return o1.getScore() - o2.getScore();                }                return i;            }        });        System.out.println("排序后："+userList);    }

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输出：

排序前：[User(name=小明, age=11, city=北京, score=66), User(name=小红, age=12, city=上海, score=99), User(name=小詹, age=14, city=广州, score=77), User(name=小龙, age=16, city=深圳, score=55), User(name=小斯, age=9, city=迈阿密, score=33), User(name=小布, age=12, city=伦敦, score=88)]排序后：[User(name=小斯, age=9, city=迈阿密, score=33), User(name=小明, age=11, city=北京, score=66), User(name=小布, age=12, city=伦敦, score=88), User(name=小红, age=12, city=上海, score=99), User(name=小詹, age=14, city=广州, score=77), User(name=小龙, age=16, city=深圳, score=55)]

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