Android时间单位换算小程序运行时总是出现异常，但又找不出哪里错了，麻烦哪位高人指点一下。
这是一个转换时间单位的小程序，如果不加if判断语句的话，timeClearButton就可以正常使用，但如果加上一条判断语句，程序可以正常换算时间，但使用timeClearButton时程序就会被强行关闭，如果加两条判断语句，程序只能执行第一个判断语句要做的事情，若使用第二个判断，程序会被强行关闭！下面是程序代码：
package lygtc.ruanjian.liuxiuxiu02;import android.app.Activity;import android.content.Intent;import android.os.Bundle;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;public class timeActivity extends Activity implements OnClickListener{ private EditText centuryText; //世纪文本框 private EditText yearText; //年文本框 private EditText monthText; //月文本框 private EditText weekText; //星期文本框 private EditText dayText; //日文本框 private EditText hourText; //小时文本框 private EditText minuteText; //分钟文本框 private EditText secondText; //秒文本框 private Button centuryButton; //世纪按钮 private Button yearButton; //年按钮 private Button monthButton; //月按钮 private Button weekButton; //星期按钮 private Button dayButton; //日按钮 private Button hourButton; //小时按钮 private Button minuteButton; //分钟按钮 private Button secondButton; //秒按钮 private EditText timeResultText; //换算结果文本框 private Button timeClearButton; //清空全部内容 private Button backButton; //返回主菜单 @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.time); centuryText = (EditText)findViewById(R.id.centuryText); yearText = (EditText)findViewById(R.id.yearText); monthText = (EditText)findViewById(R.id.monthText); weekText = (EditText)findViewById(R.id.weekText); dayText = (EditText)findViewById(R.id.dayText); hourText = (EditText)findViewById(R.id.hourText); minuteText = (EditText)findViewById(R.id.minuteText); secondText = (EditText)findViewById(R.id.secondText); timeResultText = (EditText)findViewById(R.id.timeResultText); centuryButton = (Button)findViewById(R.id.centuryButton); centuryButton.setOnClickListener(this); yearButton = (Button)findViewById(R.id.yearButton); yearButton.setOnClickListener(this); monthButton = (Button)findViewById(R.id.monthButton); monthButton.setOnClickListener(this); weekButton = (Button)findViewById(R.id.weekButton); weekButton.setOnClickListener(this); dayButton = (Button)findViewById(R.id.dayButton); dayButton.setOnClickListener(this); hourButton = (Button)findViewById(R.id.hourButton); hourButton.setOnClickListener(this); minuteButton = (Button)findViewById(R.id.minuteButton); minuteButton.setOnClickListener(this); secondButton = (Button)findViewById(R.id.secondButton); secondButton.setOnClickListener(this); backButton = (Button)findViewById(R.id.backButton); backButton.setOnClickListener(this); timeClearButton = (Button)findViewById(R.id.timeClearButton); timeClearButton.setOnClickListener(this); } @Override public void onClick(View v) { // TODO Auto-generated method stub int id = v.getId(); switch(id){ case R.id.backButton:{ Intent backIntent = new Intent(this,Liuxiuxiu02Activity.class); startActivity(backIntent); break; } case R.id.timeClearButton:{ centuryText.setText(""); yearText.setText(""); monthText.setText(""); weekText.setText(""); dayText.setText(""); hourText.setText(""); minuteText.setText(""); secondText.setText(""); timeResultText.setText(""); break; } } if(centuryText.getText().toString() != null){ //第一个判断语句 double Century = Double.parseDouble(centuryText.getText().toString()); yearText.setText(""); monthText.setText(""); weekText.setText(""); dayText.setText(""); hourText.setText(""); minuteText.setText(""); secondText.setText(""); switch(id){ case R.id.centuryButton:{ double century = Century*1; timeResultText.setText(String.valueOf(century)); break; } case R.id.yearButton:{ double year = Century*100; timeResultText.setText(String.valueOf(year)); break; } case R.id.monthButton:{ double month = Century*100*12; timeResultText.setText(String.valueOf(month)); break; } case R.id.weekButton:{ double week = Century*100*12*52; timeResultText.setText(String.valueOf(week)); break; } case R.id.dayButton:{ double day = Century*100*12*52*7; timeResultText.setText(String.valueOf(day)); break; } case R.id.hourButton:{ double hour = Century*100*12*52*7*24; timeResultText.setText(String.valueOf(hour)); break; } case R.id.minuteButton:{ double minute = Century*100*12*52*7*24*60; timeResultText.setText(String.valueOf(minute)); break; } case R.id.secondButton:{ double second = Century*100*12*52*7*24*60*60; timeResultText.setText(String.valueOf(second)); break; } } } if(yearText.getText().toString() != null){ //第二个判断语句 double Year = Double.parseDouble(yearText.getText().toString()); monthText.setText(""); weekText.setText(""); dayText.setText(""); hourText.setText(""); minuteText.setText(""); secondText.setText(""); switch(id){ case R.id.centuryButton:{ double century = Year/100+Year%100; timeResultText.setText(String.valueOf(century)); break; } case R.id.yearButton:{ double year = Year*1; timeResultText.setText(String.valueOf(year)); break; } case R.id.monthButton:{ double month = Year*12; timeResultText.setText(String.valueOf(month)); break; } case R.id.weekButton:{ double week = Year*12*52; timeResultText.setText(String.valueOf(week)); break; } case R.id.dayButton:{ double day = Year*12*52*7; timeResultText.setText(String.valueOf(day)); break; } case R.id.hourButton:{ double hour = Year*12*52*7*24; timeResultText.setText(String.valueOf(hour)); break; } case R.id.minuteButton:{ double minute = Year*12*52*7*24*60; timeResultText.setText(String.valueOf(minute)); break; } case R.id.secondButton:{ double second = Year*12*52*7*24*60*60; timeResultText.setText(String.valueOf(second)); break; } } } }}