New to java(have code) need very simple corrections

import javax.swing.JOptionPane;

public class firstProject{
	public static void main(String[] args){
	
	
	
	while(true){
	int lowerECount = 0, higherECount = 0;
	
	String sentence = JOptionPane.showInputDialog(null, "Enter a sentence");
		if(sentence == "Stop" || sentence == "stop"){
			System.exit(0);
		}


		
		for(int i = 0; i < sentence.length(); i++){
			if(sentence.charAt(i) == 'e'){
				lowerECount++;
			}
				if(sentence.charAt(i) == 'E'){
				 	higherECount++;
				}
		}//for

		
		JOptionPane.showMessageDialog(null, "number of lower case e's are: " + lowerECount +
						" " + "number of higher case e's are: " + higherECount);


		}//while				 
	



	}//main

}//class

String sentence = new String("");
while(!sentence.equals("Stop")){
	int lowerECount = 0, higherECount = 0;
	
	sentence = JOptionPane.showInputDialog(null, "Enter a sentence");

//   [ ... ]

}