java常用输出技巧，debug

package control;

import javax.swing.JFrame;

public class DebugTest {

    public static void main(String[] args) {
        System.out.println("Hello World!");
        System.out.println(123);
        System.out.println(true);
        System.out.println(new JFrame(){
            @Override
            public String toString() {
                // TODO Auto-generated method stub
                //return super.toString();
                return "This is a jframe.";
            }
        });
        
        System.err.println("There is an error.");
    }
}

package control;

import javax.swing.JFrame;

public class DebugTest {

    public static void main(String[] args) {
        int [] ints = new int[20];
        try {
            for (int i = 0; i < 21; i++) {
                ints[i] = i+1;
                System.out.println(ints[i]);
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.err.println("数组越界！");
        }
    }
}