How to use removeIf() to remove 2 conditions?-CodePudding

I want to use removeIf to remove 2 conditions , but did not find proper way to do that.

Ex. Want to remove whoes grade is below ‘B’

Code as following:

Student[] group1 = {new Student(), new Student(), new Student(), new Student()};

group1[0].setInfo("Davut", 'M', 123, 'A');
group1[1].setInfo("Ali", 'M', 43, 'B');
group1[2].setInfo("Ivan", 'M', 34, 'B');
group1[3].setInfo("Lily", 'F', 67, 'C');

System.out.println(Arrays.toString(group1));

ArrayList<Student> students = new ArrayList<>();
students.addAll(Arrays.asList(group1));
System.out.println("--------------");
Predicate<Student> condition = p->p.grade=='C'&& p.grade=='B';
students.removeIf(condition);

CodePudding user response：

The issue is with this line:

Predicate<Student> condition = p->p.grade=='C'&& p.grade=='B';

You'r asking to remove a student that has grade 'C' AND 'B'. It should be 'C' OR 'B'.

Replace with this:

Predicate<Student> condition = p->p.grade=='C' || p.grade=='B';

CodePudding user response：

Predicate<Student> condition = p->p.grade=='C'&& p.grade=='B';
students.removeIf(condition);

Should be

Predicate<Student> condition = p->p.grade=='C'|| p.grade=='B';
students.removeIf(condition);

It's impossible for a student's grade to be both B and C, so the predicate you provided will never be true.

Also, it's possible to chain together two predicates with the and() and or() methods like so:

Predicate<Student> condition = p->p.grade=='C'
Predicate<Student> condition2 = p->p.grade=='B';
students.removeIf(condition.or(condition2);
// students.removeIf(condition.and(condition2); works similarly but with logical and

https://howtodoinjava.com/java8/predicates-logical-operations/

CodePudding user response：

You also could try to do something like:

Predicate<Student> condition = p-> ((int) p.grade) > 65;

'A' char in ASCII is 65, so any letter after A, like B - 66, C - 67, D - 68 are higher.

However it is not particularly safe to do this. Because what if You pass a '@' as grade char..

I would most probably introduce a Enum with grades. And in enum instroduce a method isLessThenA() In method I would check if value is of ssome enum type and if not, would throw an Exception.

CodePudding user response：

The other answers are correct. As an alternative, why not just two calls to removeIf()?

students.removeIf(p->p.grade=='C');
students.removeIf(p->p.grade=='B');

I find it clear to read, and neither you nor your reader needs to consider whether it should have been && or ||.