（1）构造方法
Intent intent = new Intent(FirstActivity.this,SecondActivity.class);
（2）setComponent方法
ComponentName componentName = new ComponentName(this, SecondActivity.class);
Intent intent = new Intent();
intent.setComponent(componentName);
startActivity(intent);
（3）setClass/setClassName方法
Intent intent = new Intent();
intent.setClass(this, SecondActivity.class);
// 或者intent.setClassName(this, "top.longsh1z.www.SecondActivity");
// 或者intent.setClassName(this.getPackageName(), "top.longsh1z.www.SecondActivity");
startActivity(intent);
cs
