下列代码中提取年份和气温怎样执行的？

下列代码中提取年份和气温怎样执行的？

public class MaxTemperatureMapper
extends Mapper<LongWritable,TextTextIntWritable>{ 
private static final int MISSING=9999;
@Override
public void map(LongWritable key,Text value,Context context)
throws lOException,InterruptedException{ 
String line=value.toString();
String year=line.substring(15,19); 
int airTemperature;
if(line.charAt(87)=='+'){// parselnt doesnt like leading plus signs airTemperature=Integer.parselnt(line.substring(88,92));
}else {
airTemperature=Integer.parselnt(line.substring(87,92));
}
String quality=line.substring(92,93);
if (airTemperature!=MISSING&&qualitymatches("[01459]")){ 
context.write(new Text(year),newIntWritable(airTemperature))；
}