MainActivity.java

... 

@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
		}
	@Override
	public boolean onOptionsItemSelected(MenuItem item) {
	    switch (item.getItemId()) {
	    case R.id.setting:
	        setting();
	        return true;
	    case R.id.about:
	        about();
	        return true;
	    case R.id.credit:
	    	credit();
	    default:
	        return super.onOptionsItemSelected(item);
	    }
	}

	private void credit() {
		 Intent credit = new Intent(MainActivity.this, Credit.class);
         startActivity(credit);

	}

	private void about() {
		 Intent about = new Intent(MainActivity.this, About.class);
         startActivity(about);

	}

	private void setting() {
		 Intent setting = new Intent(MainActivity.this, Setting.class);
         startActivity(setting);

	}}

...