java - 计算字符串中字符的出现次数(频率)

Question

我有一个 GUI，可以计算字符串中第一个字母的出现次数。我希望它以列格式计算所有字母，例如:

这是我到目前为止所拥有的:

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;  
import java.awt.event.ActionListener;  
import javax.swing.JButton;  
import javax.swing.JFrame;  
import javax.swing.JLabel;  
import javax.swing.JPanel;  
import javax.swing.JTabbedPane;  
import javax.swing.JTextField;  
public class Index2 extends JFrame implements ActionListener  
{  
    private JTabbedPane jtabbedPane;  
    private JPanel characterFinder;  
    JTextField enterText, countText;  

    public Index2()  
    {  
        setSize(400, 250);  
        setVisible(true);  
        setSize(400, 250);  
        setVisible(true);  
        setTitle("Total Characters");  
        setSize(300, 200);  
        JPanel topPanel = new JPanel();  
        topPanel.setLayout(new BorderLayout());  
        getContentPane().add(topPanel);  
        createCharacterFinder();  
        jtabbedPane = new JTabbedPane();  
        jtabbedPane.addTab("Count Characters", characterFinder); 
        topPanel.add(jtabbedPane, BorderLayout.CENTER);  
    }
    public void createCharacterFinder()  
    {  
        characterFinder = new JPanel();  
        characterFinder.setLayout(null); 
        JLabel enterLabel = new JLabel(  
                "Enter Some Text");  
        enterLabel.setBounds(90, 5, 260, 20);  
        characterFinder.add(enterLabel); 
        enterText = new JTextField();  
        enterText.setBounds(10, 30, 270, 70);  
        characterFinder.add(enterText);  

        JButton search = new JButton("Count Occurences of Each Letter");  
        search.setBounds(15, 100, 260, 20);  
        search.addActionListener(this);  
        characterFinder.add(search);

        countText = new JTextField();  
        countText.setBounds(80, 130, 120, 500);  
        characterFinder.add(countText);
    }
        public void actionPerformed(ActionEvent e){
            String st=enterText.getText();
            char searchedChar=enterText.getText().charAt(0);
            count(searchedChar,st);
    }
    public int count(char c, String str) {
        if (str == null) return 0;
        int cnt = 0;
        for (int i = 0;; cnt++) {
        if ((i = str.indexOf(c,i)+1) == 0) break;
        }
        countText.setText("Character "+c+" occurs "+cnt+" times");
        return cnt;
        }

    public static void main(String[] args)  
    {  
        JFrame frame = new Index2();  
        frame.setSize(300, 700);  
        frame.setVisible(true);  
    }  
}

Answer 1

计算字符(假设 ASCII 字符)的一个好方法是利用 'a' 可以直接映射到数字的事实。

int[] charCounts(String s) {
  int[] counts = new int[256]; // maximum value of an ASCII character
  char[] c = s.toCharArray();
  for (int i=0;i<c.length;++i) {
      counts[c[i]]++;
  }
  return counts;
}

现在要查找任何特定元素的计数，您可以执行 counts['a']。

使用上面这样的方法预先进行计数，然后使用非常粗略的方式显示计数，可能会使代码更加整洁:

int[] counts = charCounts("my string");
StringBuilder sb = new StringBuilder();
for (char a = 'a'; a <= 'z'; a++) {
    sb.append(a).append(" occurred ").append(counts[a]).append(" times\n");
}