class Stack {
    private char content;
    private Stack next;

    Stack(char content) {
        this.content = content;
    }
    private Stack(char content, Stack next) {
        this.content = content;
        this.next = next;
    }

    Stack(char[] content) {

    }

    public void push(char content) {
        // это говно не работает
        this = new Stack(content, this);
    }
    public void push(char[] content) {

    }

    public char pop() {
        char letter = content;
        // И это тоже
        this = next;
        return letter;
    }
}