public class System{
    static class out{
        public static void println(String x){
            java.lang.System.out.println("bbbb");
        }
    }
    public static void main(String[] args) {
        System.out.println("aaaa");
    }
}

------解决方案--------------------
public static void main(String args[])
	{
		PrintStream out = null;
		try
		{
			out = new PrintStream("bbbb");
		}
		catch (FileNotFoundException e)
		{

			e.printStackTrace();
		}
		System.setOut(out);

		System.out.println("aaaa");

	}

------解决方案--------------------
忘了加format这句
public static void main(String args[])
	{
		
		System.out.format("bbbb");
		PrintStream out = null;
		try
		{
			out = new PrintStream("bbbb");
		}
		catch (FileNotFoundException e)
		{
			
			e.printStackTrace();
		}
		System.setOut(out );

		
		System.out.println("aaaa");
		
	}

------解决方案--------------------
Java code
try {
    String aaaa = "aaaa";
    Field field = String.class.getDeclaredField("value");
    field.setAccessible(true);
    char[] value = (char[]) field.get(aaaa);
    Arrays.fill(value, 'b');
} catch (Exception e) {
}
System.out.println("aaaa");