Something

     public void build ( ) throws IOException // Build tree from prefix expression    {        root = buildSub(makeNewNode());    }   private TreeNode buildSub ( TreeNode p )  throws IOException    {    	int x = (int)p.getElement();    	if((p.getElement() == '*' ||p.getElement() == '/' ||p.getElement() == '+' ||p.getElement() == '-')){    		System.out.println("calculator");    			p.setLeft(buildSub(makeNewNode()));    			p.setRight(buildSub(makeNewNode()));    			return p;    	}    	else if(x >= 48 && x<=57){    		System.out.println("number");    		if(p.getLeft() == null){    			p.setLeft(buildSub(makeNewNode()));    		}    		else{    			p.setRight(buildSub(makeNewNode()));    			return p;    		}    		    	}    	else{    		System.out.println("incorrect");    		return null;    	}