Stream flow precautions

removeIf and filter Methods can achieve filtering / The role of deleting elements .

From the function is to realize ,removeIf Yes, the condition is true Filter this element ,false The retention . and filter The condition is false Filter this element , and true The retention .

1、 Filter and collect （ Filter out those that meet certain conditions in the old set , And collect it , Come together into one newlyList）
100 There's... In the ball 10 A red ball 90 A green ball , We from 100 Take this out of a ball 10 A red ball and throw it away , That's how it feels

        List<RolePermission> newlyList = assignablePermissionSets.stream()
                .filter(ps ->