Java list集合排序

1.简单类型：

Collections.sort(list, new Comparator<String>(){
    public int compare(int o1, int o2) {
        return o1 - o2;
    }
});

Collections.sort(list, new Comparator<String>(){
    public int compare(String o1, String o2) {
        return o1.length() - o2.length();
    }
});

2.复杂类型（对象）：

Collections.sort(list, new Comparator<Emp >(){
    public int compare(Emp o1, Emp o2) {
        return o1.getSalary() - o2.getSalary();
    }
});

3.举个栗子：(根据学生成绩等级排序，A、B、C、D，把等级转换成字符的ASCII值进行排序)

public static void main(String[] args) {
	List<Sutdent> list = new ArrayList<>();
	Sutdent sutdent1 = new Sutdent();
	sutdent1.setGrade("B");
	list.add(sutdent1);
	Sutdent sutdent2 = new Sutdent();
	sutdent2.setGrade("A");
	list.add(sutdent2);
	
	for (Sutdent sutdent : list) {
		System.out.println("排序前：" + sutdent.getGrade());
	}
	
        // list排序
	Collections.sort(list, new Comparator<Sutdent>() {
		@Override
		public int compare(Sutdent s1, Sutdent s2) {
			String grade1 = s1.getGrade();
			String grade2 = s2.getGrade();
			int num1 = 0;
			int num2 = 0;
			if (StringUtils.isNotBlank(grade1) && StringUtils.isNotBlank(grade2)) { // 判空
				char[] chars1 = grade1.toCharArray();
				for (char c : chars1) {
					num1 += (int)c;
				}
				char[] chars2 = grade2.toCharArray();
				for (char c : chars2) {
					num2 += (int)c;
				}
				System.out.println("num1:" + num1);
				System.out.println("num2:" + num2);
				return num1 - num2;
			} else {
				return 0;
			}
		}
	});
	
	for (Sutdent sutdent : list) {
		System.out.println("排序后：" + sutdent.getGrade());
	}
}